Mr Smith goes to the doctors for the results of his wifes blood test.
Doc; Well we've got the test results back, but there was a mix up between two Mrs Smiths and we don't know who's is who's. One is your wifes and the other is someone else.
Mr Smith; Sorry, thats not good enough. But there must be something serious or you would just say that everything is ok.
Doc; Well, its like this. One of them has aids, and the other has alzeimers disease.
Mr Smith; Oh b@llox, well thats pretty serious. How can we find out which one is my wifes?
Doc thinks for a bit, then says, ' tell you what. Go home and pick up your wife in the car. Take her to the middle of town and drop her off to do the shopping. You go home and wait. If she finds her way back safely, don't f*ck her!