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1.
The problem that arises when two friends/acquaintances meet each other, and one prepares for a handshake, while the other comes in for a fist bump.

This usually results in a subsequent change/reversal of greeting method for each party, and in more confusing attempts to combine two incompatible hand formations.
Brad: Hey whats up Tom.
Tom: Whats up Brad.

*Brad extends his hand while Brad puts forward his fist.

Brad: Ah, I see we have stumbled into The Classical Dilemna.
by KrakenHead October 10, 2013