When you and your best friend have insurmountable differences in your friendship and you have to break up with your best bro. It includes but is not limited to, no longer speaking to one another, talking trash about one another and awkward moments of returning each others belongings
Guy 1: Yeah, we used to be tight but we had a bro-ke up.
When your best guy friend starts hanging out with a different guy and they become best friends.
Guy 1: "Dude, I went to the movies last night and I saw Kent hanging out with Bradley. And today they're going bowling together! I thought Kent was MY best friend!"
Guy 2: "Ahh, I see. Sorry dude, he totally just bro-ke up with you."