Season 6: Episode 6 - The Extract Obliteration

The Extract Obliteration: Sheldon gets excited when Stephen Hawking agrees to play him in a game of Words With Friends. However, when Sheldon starts to beat him badly, Hawking sulks and stops playing. Taking advice from Wolowitz, Sheldon throws the game and Hawking immediately beats him and starts gloating. Meanwhile, Penny enrolls in a class at Pasadena Community College but doesn't want to tell Leonard about it. When she does, he rewrites one of her papers without her consent, leaving her furious with him.