"What’s the most intellectual joke you know?"

Summarizing the results of a great Reddit thread. Example:

Jean-Paul Sartre is sitting at a French cafe, revising his draft of Being and Nothingness. He says to the waitress, "I'd like a cup of coffee, please, with no cream." The waitress replies, "I'm sorry, Monsieur, but we're out of cream. How about with no milk?”