Phase used when someone grossly overreacts to small situation or minor annoyance.

Origin: Dec 09 in D.C during a snowball fight a group of people threw snowballs at a passing Hummer, the angry driver, an off-duty detective, got out of his metal machine brandishing a hand gun, looking for the cultrits.

A crowd soon gathered and began to chant "You don't bring a gun to a snowball fight" over and over.