From the phrase, 'to have a tidy', meaning to straighten one's clothing, to make oneself neat, or presentable. In men it can also mean to adjust/reposition one's cock and balls (especially necessary on a hot day), usually under the guise of tucking oneself in.
What are you doing with your hands in your trousers? I'm only having a bit of a tidy (noun)!
by LeDiabolique April 15, 2011