Ohh, I remember that one, my mom made me turn that episode off because it was too "naughty" I guess for explaining sex, which I know NOTHING about. *wink wink*
Okay, I forgot the name of the episode, but it's when Bart plays football, and quits, so Homer's like "Since my son's a big quitter, I guess I'll be a quitter too" so he calls Mr. Burns and tells him that he quits, and starts winking, and Marge says "Homer, Mr. Burns can't see you winking over the phone. That was funny.