A man goes into a restaurant, orders albatross, eats one bite, and kills himself. Why?
The man was in a ship that was wrecked on a desert island. When there was no food left, another passenger brought what he said was albatross but was really part of the man's wife (who had died in the wreck). The man suspects something fishy, so when they finally return to civilization, he orders albatross , realizes that what he ate before was his wife, and kills himself.
(there is also a version of the riddle with an abalone instead of an albatross)