it's on

Phrase

 * 1)  A conflict is starting.
 * 2) * 1959: Girls Town (film)
 * [A man from a competing gang throws a drink in Fred's face, just before a fight begins.]
 * Fred Alger (Mel Tormé): It's on!

Usage notes
Used as an announcement of a (usually physical) fight between two increasingly hostile groups, typically stated by one of the parties to the fight.