Occurs when playing poker. When either you or your opponent goes all-in (shoves) you show down, and when you are statistically a favorite (usually heavily) to win a hand, the flop, turn, or river (any subsequent cards after the show) give the opponent the unlikely win.
Some donk cracked my AA with his K10 last night, I shoved after the turn and he called. The cards were A,K,J,5. He called and caught his river Q to give me a "sick beat."