Unlike facesitting, faceslamming involves the woman straddling the man's head and then bringing her ass down hard on the man's face. Smothering, grinding down, or continuing to violently bounce-fuck his head can follow.
Care should be taken to avoid performing this act, especially on a hard surface, as it can easily lead to the man being knocked out by the woman's slamming ass.
Alex: Well, she did fuck me later... But all that squeaking you heard? She was faceslamming the hell out of me.
Paul: ... Whoa.