F is for Frotteurism

Frotteurism is a paraphilia where the frotteur derives sexual pleasure from rubbing (usually their penis) on a non-consenting person.

This is a really rude paraphilia.  Actually it's a criminal offence.  As is ANY NON-CONSENSUAL SEX ACT.

Acting on frotteuristic desires could get you arrested or sent to a psychiatrist.  Frotteuristic Disorder is listed in the DSM-V.

The prevalence of frotteurism is debated.  However if you're a girl who's been on the London Underground in rush hour, you might predict it is very prevalent.