I'm pretty sure he's just trying to be as annoying as possible here. Brothers...
And I noticed he was trying to be extra slobbery too.
He thinks he's cute and funny. Yeah, I do too.
I think brothers are born with the annoying gene. At least she still thinks it's funny, for now.
After all that, he had to get a real kiss. I like how she is very subtly pushing him away.
Future blackmail picture.