The act of simultaneously fisting a girl's asshole and pussy using a piston-like motion. Typically, the fisting is performed by one individual, however it is not unheard of for two individuals to work in tandem. Additionally, the Detroit Fistons can be self-administered. Please consult your physician before you attempt this technique.
I think I'm gonna try the Detroit Fistons on her tonight, I've been practicing the piston motion all day.