Wow I agree with the definition above me!
Okay but anyways, boys night out also can mean a bunch of boys going out having a night on the town. Sometimes boys night out is a bunch of drunk guys with no girlfriend. Then there are guys with stupid girlfriends and they are just doing it to make the girlfriends jelous or worried. Then for the older men is just a game of poker or whatever they do!
Guy 1: Hey man! Boys night out!
Guy 2: Yeah okay cool do0d
Guy 1: Oh and BYOB
Guy 2: Dude that fucking sucks! I'm out