I agree to the awkwardness. I havent actually done it in front of my current girlfriend. I kinda think she'd like it, but maybe I'm just to shy to ask, "Hey baby, wanna watch me whack it?" Seems like I'd just prefer to make her suck me off.
I have in the past jerked myself off with a different girls hand. basically she was jerkin it, and I grabbed her hand and showed her how it was done. that was cool. And that chick definately liked it. But I didnt respect her, so i didnt care that I was basically tellin her she didnt know what she was doin.