Leonard decides to move in with Penny after he gets tired of Sheldon’s weird rules, social incompetence and insensitivity. However, he doesn’t really ask his girlfriend her opinion in his plans, assuming she’ll want to move in with him as much as he does her.
Unfortunately for the scientist, that simply isn’t the case. Penny doesn’t want to hurt his feelings, though, so she tries to convince him that Sheldon needs him. She calls the two men “a cute couple” and then compares them to Burt and Ernie of “Sesame Street.” Penny said they even try to teach her words and numbers.
Leonard still doesn’t take the hint. It all comes up in a big blow out in the hall involving Leonard, Penny, Sheldon and Amy.