Green’s Dictionary of Slang

(UK/US police) the action of the frotteur, using the anonymity of a dense crowd to rub one’s penis against the nearby buttocks of defenceless women; thus bustle-puncher/bustle-rubber, a frotteur or one who caresses women’s buttocks in a crowd.

1970		‘Metropolitan Police Sl.’ in P. Laurie Scotland Yard (1972) 321: bustle puncher, a: one who caresses ladies’ bottoms in a dense crowd.
1972		J. Wambaugh Blue Knight 26: I guess even the wienie waggers and bustle rubbers gave up sneaking in.
1977		D. Powis Signs of Crime 176: Bustle-punching The practice, not uncommon in dense crowds, of a male rubbing his penis against the buttocks of females. The penis may or may not be exposed.
1989		J. Morton Lowspeak 32: Bustle Pinching, or Punching – the practice of rubbing up against women.