When I teach introductory computer science courses, I like to lighten the mood with some humor. Having a sense of fun about the material makes it less frustrating and more memorable, and it's even motivating if the joke requires some technical understanding to 'get it'! I'll start off with a couple of my favorites: Q: How do you tell an introverted computer scientist from an extroverted computer scientist? A: An extroverted computer scientist looks at your shoes when he talks to you. And the classic: Q: Why do programmers always mix up Halloween and Christmas? A: Because Oct 31 == Dec 25! I'm always looking for more of these, and I can't think of a better group of people to ask. What are your best programmer/computer science/programming jokes?