I am human, I know I will make mistakes in class. I have been teaching for 5 years now and still check to make sure my fly is zipped before entering the classroom. That would be the worst! Humor is the answer, everytime. It is important to teach the students to laugh at themselves as well. I am the perfect example. If I miscount handout copies, I blame my secretary by rolling my eyes and saying sarcastically, "my secretary can't count"! My students know I don't have a secretary. I feel redeemed in their eyes if I can crack them up. They also forget your mistake.