Leonard: Hi, Howard. Howard?
Howard: Sheldon.
Sheldon: Howard is employing a schoolyard paradigm in which you are, for all intents and purposes, deceased. He intends to act on this by not speaking to you, feigning an inability to hear you when you speak and otherwise refusing to acknowledge your existence.
Leonard: That's just ridiculous. Why are you cooperating with him?
Sheldon: I don't make the rules, Leonard.