A "bro moment", an occasion where two 'bros' are bonding on something between them that is common ground.
Bro 1: Dude, that chick's body is so bangin'.
Bro 2: I know right, I wish I could get on that shit.
Bystander: You know, she's not the only chick to have a body like that.
Bro 1: Man, don't ruin our bro-ment.