Allow me to borrow/modify something I posted on the #631 thread....
This is what Naruto looks like when he's joking / not serious / lying about his relationship with Sakura. You can tell he's lying not only by his words but by his expression and posture as well. There's always some kind of "tell" when he's joking. He's got a cheesy smile, or he's doing something completely outrageous, or he's sneaking around, or he's generally being a doofus.
Then there's #631....
We get a significantly different expression and response from Naruto. He is as sober as a judge here. The look on his face is serious. The words he uses are serious. There's no hint of joking whatsoever. HE IS NOT JOKING.
I can understand why anti-NS folks would want to downplay this moment as a joke or something casual, but I can't understand why any NS fan would say he is joking here when he clearly is not. He's not even smiling, for crying out loud!
The comment Naruto made in #632 -- "I'll never, never turn on Sakura-chan again... she'll pulverize me...." or "Ne-never again... I can't ever poke fun of Sakura-chan again... otherwise she'll turn me into a stain...." (depending on the translation) -- WAS a joke. You can tell by "lady lips" caricature of his face and the overall silliness. He's referring to all the stupid jokey crap he's done over the years to get a rise out of her -- the Oiroke no Jutsu, teasing her about being strong, etc. -- NOT his feelings for her.
Remember his reaction in #469? How he told Sakura -- twice -- that joking about something like loving him or choosing him over Sasuke wasn't funny? Right. But we're supposed to believe he turned around and "joked" about Sakura being his girlfriend to his father? Please.
As far as I'm concerned, trying to link the obvious joke in #632 to Naruto's answer to his father in #631 is either willful blindness or a desperate attempt to invalidate Naruto's declared feelings for Sakura.
I bow to you sir