The bronco is performed when a couple is having sex doggy style, made popular by
the T.V show
Dexter. When the bottom is getting really into it, you hold onto their hips and say another person's name. The bottom then will try to "buck" you off, much like a horse.
Example:
Conversation about Bronco, taken from Dexter:
Angel Batista: She's a butterface.
Dexter Morgan: What's a butterface?
Angel: You know, compadre. She's got a hot body - but her face.
Dexter: Oh.
Masuka: How great would it be to pull a bronco on her? Yeah? Yeah?
Angel: You do it doggie-style. Right? And just when she's getting into it, you grab her by the hips, and you yell another woman's name, and, bam, you're riding her like a bronco, because she's trying to
buck you off.