Teaching science is hard. You have to manage a large class with different learning styles. There are always conflicts and you have to keep everyone on task while working on experiments and demonstrations. It can be daunting, but not always.
Sometimes it's okay to show a sense of humor. After 25 years of teaching I've found this to be true. Humor can be the one thing that gets a student engaged with the material and focused on the labs and experiments at hand.
Show your sense of humor (and smarts) to your students this school year with one of these great funny science teacher t shirts.