A slang term used to discreetly refer to a man's erection. The owner of the Jim may or may not realize he's standing at attention - you can either try to save his dignity or point and laugh. The term is often used in the company of women or others that are not privy to its true meaning.
Jimbo, my brother, I tried to save you! ...When you left that room, you had the most obvious Jim I've ever seen. You almost smacked poor Kate in the face with it!
by Capn Morgan December 28, 2008