Opposite Day

“Opposite Day, also called Backwards Day, is a game usually played by children. The game begins when someone declares that it is "opposite day” On Opposite Day, everything is the opposite of what it usually is.”
Every year: April 21

Everything is opposite no matter what

Person 1: Can i fuck your cat?
Person 2: No
(what person 2 really meant was yes)

Person 1: Is today opposite day?
Person 2: No
(what person 2 really means is yes)