!! OMG, he's naked: Johnny Galecki !!
To wrap up the former-child-star theme I've been going with this week, guess who's decided to show the full monty in the currently running play The Little Dog Laughed? One of his early roles was Clarke Griswold's son Russ in National Lampoon's Christmas Vacation (which is my favorite Christmas movie ever), and he later played Darlene's boyfriend David on Roseanne.
Johnny Galecki is his name, and he has a huge thing between his legs. So huge, in fact, that it has startled audiences. See if after the jump [NSFW].
(Thanks to Clinton for the photo!)