When you, as a younger man/woman/
whatever, groom an elder
gentleman/gentlewoman/gentlewhatever into pursuing yourself despite their moral objections. Hence turning them into a
nonce.
Person
1: Did you hear about what happened to
Lewis?
Person 2: Ali, through reverse noncing, got him into bed
Person 1: No fucking way,
Lewis is like 10 years older than him and not into younger men.