That's Why They Call It Ball Room
Two and a Half Men Season 7 Episode 10 (12/07/09)
Chelsea manages to convince Charlie to take dancing lessons, while his mother convinces him to ask her for a prenup. While dancing, Charlie takes advantage of his brownie points and asks for the prenup, and Chelsea is more than okay with it. Turns out she owns several high-end apartment buildings and wants to protect her wealth. Charlie becomes devastated that not only was she hiding a secret from him (and never picked up the check), but that she must be marrying him for something other than his money. Charlie can't fathom what that could be. When Charlie is sent to sleep on the couch, he kicks Alan out of his bed and sends Alan to the couch. Chelsea comes out to apologize and ends up laying naked with Alan. Charlie is so thrilled to hear Chelsea admit she was wrong for keeping a secret that he merely gives her perv brother a wedgie and heads to bed with his fiancee.
Meanwhile, Alan spends the episode watching his and Judith's wedding video as they do a hilarious dance to "I Had a Time of my Life." We also get to see Charlie come back from sleeping with Judith's sister to give the best man toast.
The episode title was used by Charlie when he practiced dancing with Alan, who told him to keep a safe distance from the groin... or leave some ball room.