Simple, bare back blowjob to completion, no stopping and swallowing. Alternatively, before he blows his load (to use the vernacular), whip it out and jerk his man juice off all over your face.
A tall order for the first time around, but that WILL DEFINITELY blow his mind.
Why? Women don't do it as a rule. It's hardcore pornstar action that men pay good money for as precious few regular women will do it.
Go nutz, show him how much you want his genetic material.
