Yours, Etc.: Origins and Uses of 8 Sign-Offs
1933, from French frottage "rubbing, friction," from frotter "to rub," from Old French froter "to rub, wipe; beat, thrash" (12c.), from Latin fricare "to rub" (see friction). As a paraphilia, it is known as frotteurism.
frottage frot·tage (frô-täzh')
The act of rubbing against the body of another person, as in a crowd, to attain sexual gratification.
The inducement of sexual pleasure by rubbing up against another person; masturbation by rubbing against another person (as in a crowd)