This is typically undertaken by a group of friends who are all in committed relationships, and wish to get away from womanly things, and eat pizza with their dude friends.
P2: Uh sorry guys, I have to go to bed bath and beyond with my girl so we can pick up some lavender bath soap.
P3: Fuck that shit dude, bro-night is man-datory. You'll be there, and you'll be drinking fucking whiskey.
P2: You knnow what? Fuck yeah, I'll be there! Bro night!
P1: Bro nght!
P2: Bro night!
Joe: Oh damn, are you inviting that chick over?
Kyle: No way! I was going to call up the bros for an epic bro night. I was thinking we'd get drunk and moon cars on Sunset Blvd.
Joe: Let's do it!