After suffering from bum dew for a prolonged period, a small stream or river can form, know as a bum river. Light coloured trousers (pants if you're American) should be avoided.
A bum river can sometimes be seen on leather car seats on a hot day or when a lard arse (somebody who regularly attends weight watchers and McDonalds) attempts to exercise.
by TW_h900 March 9, 2007