"It's okay! I always get on the floor, and stick my tush in the air for a sexy pose...IT'S FOR ART!"
I'm guilty of having a mirror on hand and making weird faces as I draw --- "Quick, press down on the medulla oblongata! Five bucks says he smells burnt toast!"- Sam ("The Adventures of Sam & Max: Freelance Police", Ep.5- "They Came From Down There")
Amusing as this is, it's not every day I hear about an artist using oneself as an art model, except for facial expressions or something.
If I ever want to be that sure about a pose, I often use one of those little artists' mannequins. However, there's only so much posability in those things, so I just let my imagination fill in the blanks.
I may at least look at my own hand to get hands right, though.