No more Mr Nice Guy - Idioms by The Free Dictionary
no more Mr Nice Guy
no more Mr. Nice Guy
An expression indicating that one is no longer going to behave in a pleasant, tolerant, or carefree manner. OK, no more Mr. Nice Guy. The next person to speak out of turn gets detention.
no more Mr Nice Guy used to suggest that you will stop being lenient and begin to adopt more severe measures.
References in periodicals archive
Although he doesn't smoke or drink very often, he says from now on it's no more Mr Nice Guy