A Bro is mostly use as a hidden code name for being gay, usually a big group of males around the ages 14-16 called as "the bros" of a high school, are just a big group of ashamed gay guys. They remain single but hook up with lots of girls, tell they are all alone with each other to have gay parties. This guys are usually really good looking and don't look gay at all. But trust me they are totally gay.
Bro 1: "Hey Bro isn't that girl over there super hot ass hell, I'm getting a blow job from her tonight.
Bro 2: *whispers* "I thought I was gonna give you one tonight"