Don't have a cow

Don't have a cow is a humorous cautionary phrase, dating from the late 1950s at least, possibly of US origin. It appeared in the 1984 movie, "Sixteen Candles". The metaphoric warning means "don't get so worked up." If one pauses to reflect on the physical aspects of a human being giving birth to a full-grown cow, one can see what this phrase alludes to in terms of emotional expressiveness. Prior to "Don't have a cow," the phrase was "Don't have kittens" (or "Don't have a cat"). A variation in the past tense is also used when someone has already become worked up, e.g. "She had a cow when she found out he'd been smoking."

Bart Simpson used the phrase "Don't have a cow, man!" as a catchphrase in early episodes of The Simpsons. Shaggy Rogers from Scooby Doo uses this phrase often.