"The Switch" Season 6, Episode 11

Elaine let's a potential employer borrow Mr. Pitt's tennis racket, but finds it difficult to get it back later. Jerry's girlfriend doesn't laugh - ever. But her roommate does. George comes up with a way to pull off the switch - Jerry will suggest a menage a trois. George suspects his girlfriend is bulimic, so he gets Kramer to contact his mom who is a bathroom maid. George then finds out Kramer's first name!