A sexual act that must be performed on the hood of a car. It does not require an actual Ford Mustang. To pull off the Mustang Sally a girl must be fully naked, laid out tits flat on the hood. Her legs remain able to touch the ground, and may stand herself up. A guy must fuck her doggy style in either the vagina or asshole. The final touch to the "Sally" is to pull out before ejaculation and cum on the hood beside her face. You then get behind her, grab her hair at the back of her head, and slam her face into the pool of resting semen.
"Dude, me and my girl were in my car and I decided to give her the mustang sally."
Friend- "Did she get pissed?"
"Yeah, ...I don't think I'll be seeing her again."