A softcore pervert. Someone who is at the early stages of becoming a "pervert" later in life. They might do things that other people around them consider 'naughty-minded' or 'off-taste' for the current situation.
A prevert is a person who pre-empts a pervert by doing to the pervert what they would have done to them, e.g. when a ballerina takes an illicit sniff of a foot fetishists loafer or when a child rapes a paedophile
"Mrs. Robinson? Mrs. Robinson? Hi, I'm sorry to have to tell you this but your son Billy molested me last night. Molested me badly."