A column purporting to identify the best physics jokes appears in this month's Physics World magazine. The Diary particularly likes the following, sent in by Ruth Hamilton of the Yorkhill NHS Trust.
A lawyer, an accountant and a physicist are discussing whether life is better with a wife or a girlfriend. The lawyer declares: "A wife is better because of the help she'll be to your career." The accountant disagrees: "Nonsense, a girlfriend is better, you can keep your independence." They turn to the physicist, who says: "It's better to have both. That way, the wife thinks you're with the girlfriend, the girlfriend thinks you're with the wife, and you can be down at the lab."