Naruto was not joking in 631, when Naruto is joking, when he's being silly, it's obvious. His facial expressions, his body language give him away, Naruto as drawn during those panel exhibited none of those characterstics first of all, and second of all Naruto would have to be a pretty terrible person to joke about that in front of the entire army, when the question wasn't addressed to him, to his father with whom he only has a short amount of time, and when the other girl who confessed to him and who just lost her cousin is right there hearing and watching it all go down. Naruto isn't a terrible person, he is so good that despite being a ninja he talks people down rather than killing/forcing them to change his mind. Naruto wasn't joking, I really think individuals who think so need to re-read the manga as a whole while paying specific and special attention to how he drawn during the instances under which he is joking. Also, Naruto walking away from Sakura because her "crimes" are unforgivable? Another misinterpretation of Naruto. First of all, her crimes weren't unforgivable, second of all let me just say that I find it very telling that so many accept that Naruto will forgive Sasuke for everything he's done, but not Sakura? Not surprised by the double standard, especially given how this fandom discusses female characters in general (and Sakura in particular).
Real girl here, who has worked as a health educator (and has been exposed to the personal thoughts and lives of many females), who has worked as an educator specifically with teenaged girls, and IMO Sakura is extremely realistic especially when taking her age into account. These are my thoughts based off my personal and professional experiences.
When thinking of Sakura we have to keep in mind that she is very young, only 17, men and women much older than her have far more screwed up views when it comes to relationships, but the younger an individual is and especially during the teenaged years (and until one is about 23-25) an individual's actions and decisions are particularly confusing, are clouded my emotional instincts and are often not thought through (this has to do with actual brain development, the frontal lobe which is responsible for our ability to consder the consequences of our actions only fully develops when we're around 23-24). So, even though many people think of 17 year olds as "almost adults," the fact is they are not and out of Team 7 Sakura has always been the most "human" character, the character who responds in an age appropriate manner. And yes, she's a trained ninja and that's something we should consider, but we should remember that it's been mentioned over and over again that the Shinobi system is flawed, and one of the flaws is that children are trained as killing machines. It's better now --after the establishment of the village system-- but it's still extremely imperfect, and frankly whether it's specifically mentioned within the manga or not it is problematic that 17 year olds are (or were) leading the battle for some time.
As to the question of what she's thinking, what one must realize is that Sakura isn't thinking, but she's feeling, and her emotions have been so jumbled that she doesn't know what she' feeling and because she doesn't know what she's feeling she can't even begin to analyze what she is thinking.
Now, isn't that confusing to read? So, if it's confusing for use to read, think about how much more confused she is. She's the one who is actually going through whatever feelings she has, and she's confused. Basing her off the parameters of the manga, as far as she knows Sasuke is the one who complimented her forehead? That seems silly to us, and it is silly, but Kishi had Kushina specifically mention that she fell for Minato because he complimented her hair --complimented a portion of her body for which she was bullied. Why is that important? Because Kishi established that a character he created to be Naruto's mother, but to also be a simplified version of Sakura fell for the first male who lifted her up from her misery. That's the Sasuke Sakura is holding onto, not Sasuke as he is or as he was, but Sasuke as she saw him because of Naruto's trick.
Now, let's look at her feelings, her reactions, and her actions towards Naruto. Everything she has done in part 2 --particularly in later chapters-- screams that she loves him and that it's very likely that she is in love with him, but for whatever reason she will not and/or cannot consider that possiblity. Why is that? There are many possible reasons, and chances are there is a combination of reasons.
- As I mentioned before, she's obviously still hung-up on caring for the person she thought Sasuke was. If she "loves" him, how can she "love" someone else. Of course, it is entirely possible to romantically love many people simultaneously (often for different reasons, but not always), but this is a concept that difficult for teenagers --especially emotional tennagers-- to understand.
- Just like Naruto feels undeserving of Sakura's feelings (until he can keep his promises to her), Sakura feels undeserving of Naruto's feelings. She is unworthy of him, that's the only reason for her to say "the idiot is in love with me," some will misinterpret that as Sakura expressing her dislike of Naruto, but that is incorrect. Sakura is expressing the fact that she feeling unworthy of Naruto's love, of the hero's love. In that moment, he's an idiot because he loves her. In fact, Sakura would probably agree with everyone who is hypercritical of her, she'd probably be the most hypercritical of all and until she gains some confidence with respect to who she is on a personal level, she'll continue to feel unworthy. At the current stage she is currently (with regards to her personal self, not professional self), she's probably the first person who would say that she is undeserving of Naruto, and she'd probably be the first person to try to set Naruto up with someone she feels would be deserving of him.
- Because of her unresolved feelings for Sasuke, and because of the feeling that she is undeserving of Naruto, she never actually considers her feelings for Naruto. She never fully explores what she feels for Naruto, what Yamato and Sai are insinuating when they talk to her, what it means when she's so emotional that she runs towards him and let's him off the hook for his promise (and states that she'll save Sasuke for him), she never considers why on an emotional level when Konoha was destroyed that she felt Naruto was the only person who could save Konoha, she never considers why she's focused on Naruto's well-being while everyone else is focused on Naruto's prowess (or the need to reach Naruto's level); and before someone claims that she must have considered her feelings before the confession I would say that she did not. Before the confession it's obvious that she's doing her best to hold back her emotions, and she's operating simply to protect Naruto, prevent Sasuke from becoming an even darker person, and she's operating in such a way that nobody else will have to deal with Naruto's hatred if they are successful in "mission kill Sasuke." What people fail to understand is that when Sakura knocked the boys out, she did so so that Naruto wouldn't be alone, and so that Konoha would retain it's hero. Just like Naruto said to Sasuke that he would face all of Sasuke's hatred, Sakura wanted to be the only one forced to face Naruto's hatread/anger, and the only person Naruto would have to write off.
Now, precisely what does all of that mean? That Sakura is unsure of her feelings, Sakura is confused, and she's not ready for her feelings to be clarified to herself. Is that realistic? YES. That could be realistic for anyone, of any gender, of any age but is especially true of a girl who is 17. Think about it, how often are we confused about our feelings, about how to react to a new situation. Then, place yourself in extremely high stakes, your way of life is being threatened, your autonomy is threatened, several people are after the person you rely on the most (they want to kill him to use something that was forced into him), your home has been destroyed (at least physicall) --not only is Sakura unable to consider her feelings for personal/emotional reasons, but she simply doesn't have the time to focus on those relatively trivial matters, that's not a priority for her at the moment, and it really shouldn't be (people still dismiss Sakura as a fangirl, but since at least the Pain Arc she has only considered romance when she was forced to do so/when it was brought up to her, that's actually an exceptional sign of maturity).
Lastly, I want to address the notion that it's unrealistic that Sakura would hold onto her feelings for Sasuke considering all that he has done to her, to Naruto, and in general; frankly I wish that were true, but unfortunately our emotions, hormone, and mental chemicals are extremely strange. If one examines how Sakura operates with respect to her "relationship" with Sasuke, one would notice that she displays many of the characteristics of a battered person --she's submissive to a fault, she tries to change herself for him, she knows he's bad for her but she can't let go of him-- any many other things that I'm too tired to think of. It's not logical for her to retain her feelings for him, but our emotions (especially when we are confused by them) are not logical, they are anything but. Obviously Sakura wasn't in an actual relationship with Sasuke, but given the circumstances and given her specific actions I'm not sure that matters --after all, in this very manga we have a character who has some sort of self-inflicted co-dependency on Naruto (I mean Hinata). It seems that just like a victim of domestic violence, Sakura feels some sort of responsibility that seems to shame her into remaining "loyal" to Sasuke --she knew something was wrong with him but was unable to stop him, she tried to change for him but that wasn't enough, she brought him flowers and food while he was in the hospital but even that wasn't good enough it triggered her, she tried to kill him so he wouldn't cause more harm but she was too weak to do so (far too stuck on the past). On some level, she seems to think that some of Sasuke's actions are her fault, so what would it mean if she let go, moved on --as if to do so would be the equivalent of ignoring her responsibilities.
tl;dr: Sakura has extremely confused in terms of romance, and she has a bit of self-hatred as well...though we don't want to face it, all that is pretty realistic especially when considering her age (though can be pretty realistic for much older individuals as well).
I hate it despite of having durians in my country. 
Ugh, sorry, but that REALLY irked me. He was just telling her to effin' rest, and I found that perfectly reasonable—she was fighting and healing countless people nonstop for like two days, and had just finished up healing Naruto from an exhausted state back to 100%, and also had NO idea about the Byakugou Seal of hers. Like, kitten, what do you want from him? So many times I've seen outright antipathy for Naruto from the SS fandom, saying Naruto treats her like a baby (???) and praise Sasuke for "telling her like it is"! Tough love! Like hell they get mad because Naruto is protective of her (a common trope in shounen manga—it's not like he does it in a suffocating way, anyway), and it's like they try to find reasons why Sasuke is better for her. :\ urgh it annoys me
It makes me want to type up a damn essay on the whole thing.
Sorry.
