Well the thing about the arrogance and selfishness is, look at his life; last movie he made peace with his aunt about Uncle Ben thus things are good, MJ finally knows the secret and they're close and in love, according to the opening dialogue he able to balance his studies with crime fighting now and finally he's not a "meanace" he's a hero and is actively celebrated. I mean look dude, now they loved Pete the way real live comic fans love him. He finally felt like he was making a difference and having people realize it.
So what does this mean? Well he's arrogant and having fun and he's trying to play it up to the crowd. He says kiss me, but he really should of said "Hey gimme a peck on the cheek, it'll be great! The crowd wants it!" But he obviously went to far. He probably rationalized it in a way that another poster mentioed: "Well, MJ acts and probably has to kiss people for a role, I'm just acting as Spider-man and that kiss doesn't mean anything"
I think it was a totally stupid move, but I don't think it was blazingly out of character.