To eat out a girl with such speed and ferocity that her body shakes uncontrollably and she ultimately ends up in the hospital. In order for this to happen the speed of the tongue must be around five times the speed of sound. Hence "mach five." Originated in Orlando, FL.
Symptoms of being mach fived:
*lying in your own pussy juice
*some serious hospital time
CAUTION: This requires years of specialized training as there are only a few men in the world who can do this. Men have died attempting this. Use extreme discretion when attempting to Mach Five your next girl.
Girl 1: Damn he really ate me out well last night. I was lying in my own pussy juice and couldn't stop shaking for hours.
Girl 2: God damn girl. I gotta get me a mach five.