usually performed while watching porn, but also applicable while watching live sex at a party
the act of matching the penetration depth of cock in observed fornication to the depth of one's own cock in one's own hand or other cock stroking deviceballs deep
in observed fornication pull hand down to match either to base of cock or to the limit of stimulation of hand
boxers all the way down, lube ready, porn site loaded and porn playing, reality melts away pumping cock in sync, usually jizzing before video ends
repeat until unable to get hard again
in lieu of fornicating.