To hastily clean your manhood in the basin of a pub’s toilets in preparation for a forthcoming sexual act with someone you’ve just met.
Dave hoped the bird he was giving a ride home to would give him a blowjob on the way so he had a gentleman's wash
the washing of the male member in the sink usually in the toilets of a pub/club before the act of sex with a one night stand or a 10 pint princess
i've just pulled best go freshen up and have a quick gentlemans wash in the bog
The washing of ones genitals, usually in a pub toilet, before having casual sex after realising one hasn't bathed in a while.
Shortly before taking a girl into the car park for a good seeing to Jeremy went to the toilets for a Gentleman's Wash.
washing of the male genitalia in the sink
Tim didnt have time for a shower, so he got his fella out for a "gentlemans wash!