Pesce d'Aprile! (April Fish!)

http://italian.about.com/library/weekly/aa032801a.htm

In Italy, as in much of the world, April 1st is traditionally a day of practical jokes, pranks, and silliness. The origin of this custom is ancient and ambiguous, but one thing is certain: much buffoonery and hilarity will take place.

The traditional pesce d'Aprile (April Fool's trick) in Italy consists of a youngster surreptitiously attaching - with the help of tape or glue - a paper cutout of a pesciolino (small fish) to the rear shoulders of a school companion. Then everyone jokingly questions: L'hai visto?—Chi?—Il pesce d'Aprile! (or Have you seen?—Who?—the April Fool!) and makes derisive remarks about the victim.