You then proceed to jump on your mates back and hold on for as long as you can, Riding her like a bull waving ones arm back and forth.
Not needed but accommodates the situation is a hat, preferably a cowboy hat.
Steve: "Did you hear what josh did last night"
John: " No, what happened?"
Steve: "Well he hooked up with Tracey and we did a rump back rodeo"
John: " Nice, how long did he last"
Steve: "At least two minutes"
John: " She must be pissed"