Manslap - when a grown man whines, bitches and moans to a point where you as a man would need to open-hand slap another man. A necessary gesture and action to quickly check a man and put him in his place, undeserving of a typical punch.
I went out with Brad the other night and he was just being annoying...Whining and complaining about nothing so I had to manslap him and check him real quick. He deserved it.
To be so angry with another person of any gender that you feel the need to punch them with an open palm. Used as a replacement for bitchslap when trying to be less sexist and misogynistic.