We have been using the word FROT since the mid 90's, when it used to mean "styling" or "going off" - back then people were just "frotting out" (getting excited about cool things), and getting "frotty" (enjoying themselves).
Rather like the word "gay" was hijacked by homosexuals and deemed to mean homosexual rather than happy, the word "frot" has to some extent also been hijacked by homosexuals and deemed to mean men rubbing their penises together. It was actually first used in the pervy sense to describe train frotters - men who rubbed up against women in crowded subway trains.
