Term used to describe an odd doggy style method. The male leans down over the female during sex then strongly punches the girl twice in the kidneys. The male must hold on while the female tries to "buck off" the guy. Any version of the bucking bronco must be witnessed by at least 2 people. And the record is 26 seconds.
"Dude, I'm taking this bitch I met home and I'm going to do the bucking bronco. I need you guys to witness it!"