Seinfeld: The Switch

Jerry wants to make the switch from his girlfriend, who never laughs, to his girlfriend's roommate. George comes up with the idea of a menage a trois so that Jerry's girlfriend will be offended and break up with him and the roommate will know he's interested, but it doesn't work out as planned. Elaine let's a potential employer borrow her boss' tennis racket which leads to trouble. George is dating a model whom he fears has an eating disorder so he enlists Kramer's bathroom attendant mother to spy on her. It is Kramer's mother that reveals his first name- Cosmo.