The bronco is a sexual encounter that involves a guy, his girl and all of his buddies. Before the encounter, 4-8 of the buddies hide in closets and other places in the room the encounter will occur. The couple enter the room and go at it. When the girl is on top, all of the buddies jump out, turn the lights on, and start cheering like it's a rodeo. The object is to get her to stay on for 8 seconds.
That bronco you pulled last night was the most fucked up thing I've ever seen!