Amy: I don't understand. What difference does it make if Leonard goes to Wil Wheaton's party?
Penny: Wil Wheaton is Sheldon's mortal enemy.
Amy: "Mortal enemy?" Sheldon, I know you're a bit of a left-handed monkey wrench, but you really have a mortal enemy?
Sheldon: In fact, I have 61 of them. Would you like to see the list?