IIRC the first two times that he does it in the ready room -- after he's been given the Q powers in "Hide & Q", and when he's being questioned by Remmick in "Coming Of Age" -- you could argue he's being arrogant and aloof. In the former instance he's just being a dick and trying to show Picard who's the boss, and in the latter instance he might just be trying showing his disrespect for Commander Remmick.
But after that? Well, he's still Will Riker. So chances are pretty good that he's just generally being an asshole.