Pokey Bum Wank - To masturbate while inserting a finger/object e.g. vibrating razor handle up your arse.
Chris enjoys a good pbw at the office desk...
A PBW (or 'pokey-bum wank'), often a taboo subject, is the simple act of masturbation glamorised by the insertion of one or more fingers into the anus.
'I had a classic bachelor evening: Strawberry Pop-tarts and a PBW.'