The getting up from being seated and doing it backwards. Keep 'em swinging, Riker.

Riker? I just met her!

swag indeed.

I wonder if a few of those was so he didn't have to walk out of the frame to sit down.

Just do a left-cheek sneak, Ryker. You're not fooling anyone.

He actually goes out of his way to do it. I think he has a mental problem.

This is probably explained in a 10 page essay linked from the 50 page article relating to "Chairs in the Star Trek Universe" cross-referenced and indexed on Memory Alpha.

Total PUA.

Beware the live straddle!

It's like...it's like he has to take a big ceremonial crap everytime he sits down. Or gets up.

In space, no one can hear you swag.

Except for Riker. They can hear his swag from the Gamma Quadrant. #nerdhumor #illshutupnow

There actually is an explanation for this: Jonathan Frakes has a bad back, and since filming is repetitive, things as simple as standing up or sitting down became extremely difficult for him, so he had to figure out ways to adjust. The way Riker sits down is one of them, but another famous one is the Riker lean.

http://rikerlean.ytmnd.com/