A reverse missionary position where the girl is on top and the guys legs are up over her shoulders. In this position the girl has to do most of the thrusting work so she really has to want it, thusly the naughty nun. Can be difficult especially for couples with big height difference
"So how was last night with that girl you left the bar with?"
"that girls raunchy we were just getting started and she turned naughty nun on me"