During sex...

[Mystyrion]

I can't even go to sleep with my socks on.

Only time you should be banging with your socks on is like in the car or something like that.

Pretty much this.
If I don't have shoes on my socks will never be on my feet.
I can't stand having socks on.

That being said I have had sex with my socks on once (yes, me, not the girl. Don't have a fetish for it). They were my high school football socks, it was winter I was cold. Couldn't be bothered with taking them off, more important things were being done.

EDIT: Also I just walked in on my roommate and his girlfriend having sex. hahahahaha.
Awkward.

[Dranzer]

I've never really given much thought to it. I either take them off, or leave them on depending on how shit got started in the first place. I will say that I tend to misplace my socks when the sexing isn't at my place. I've also lost my boxers once, or forgot to put them back on after; one or the other I haven't seen them since.

@Rowan - Your post reminded me of the movie Funny People; Adam Sandler's banging this one chick and she asks him to make a merman noise.

^I've always wanted to do that just to see what someone's reaction would be, but I keep forgetting...