A little disappointed that the Urban dictionary doesn't explain the origin of the phrase, just gives plenty of examples of use. You are right that it is probably not PC but we will run out of expressions that we can use soon for fear of offending someone. They need to develop an "edit" app for us so that whatever we are about to say can be modified by the app before it comes out of our mouth... or we type it. Surely this PC thing has gone too far now and a modicum or common sense needs to be applied!