Penny: Well, Sheldon you are his friend. Friends give each other presents.
Sheldon: I accept your premise; I reject your conclusion.
Wolowitz: (quietly to Penny) Try telling him it's a non-optional social convention.
Wolowitz: Just do it.
Penny: It's a non-optional social convention.
Sheldon: Ahh, fair enough.
Wolowitz: He came with a manual.