Wow, it's difficult to pick just one!
"Major Boobage". I don't usually memorize episode titles, but of course that one stuck. It was the tribute to my favorite animated film, "Heavy Metal".
But usually my favorites are the ones where Randy (Stan's dad) goes way overboard with things, completely overacting. Like the one where he feels he has to pick a fight during all of Stan's ball games. "Wha-...What'd'yawannado huh?...W-What'd'yawannado?"
Or the World of Warcraft episode when his character dies at the end and he completely hams up his death scene. "Staaannnn....Staaannnn..."
Or the one where he purposely gets testicular cancer so he can get medical marijuana. Haha And he starts using his balls as pogo balls, bouncing down the street. I could not stop laughing!