I had noticed Frakes doing "the Riker chair maneuver" before, especially when he does it in the ready room. But I'd never noticed it was so widespread, and that he was still doing it in season seven!
All the lurching and leaning can be explained by Frakes's height and back problems. But the chair as a pony.. didn't anyone notice how retarded this looks?
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.
I'm a tall guy (6'3") as I think Frakes is. And notice all those chairs have low backs...probably having to do with prop design. It is actually easier when you are that tall to swing your leg over the back of a chair than it is to pull the chair out, sit down and pull the chair back up. So I bet it actually became pretty natural. When you are watching the clip, some of them are pretty easy to miss because it is effortless for someone that tall.
Puts a whole new spin on the scene in Generations when he says, "I always thought I'd get a crack at this chair someday." --Sran
What annoys me is all the time he sits in his Bridge chair with his legs splayed open. It's like he's putting his "assets" on display while pretending he's not wearing any clothing over them. Newsflash: After seeing Schwarzenegger in the first Terminator movie, I doubt Jonathan Frakes/Will Riker would ever be close to qualifying for preliminaries, never mind actually being in the contest. He looks like he's intending to piddle on an invisible fire hydrant. And the ship either needs taller chairs, or they need to get Riker a horse. Agreed. Picard should have asked him if he needed to schedule holodeck time to review basic military decorum and posture.
Which part of my post confuses you? Riker acts like he's always putting his "masculine assets" on display, regardless of how much clothing he's wearing. Arnold Shwarzenegger's nude scene in the first Terminator movie has forever spoiled me for all other such displays, clothed or not.