Humor in the classroom is one of the most effective tools you have in your teaching arsenal. It can diffuse tense situations. It can make you appear more human to your students. Even if your jokes fall flat, students will still appreciate your attempt. With that said, sarcasm is an area of humor that can really create more problems. Many students will not understand that your sarcastic remarks are only meant in jest. It is probably best not to use sarcasm at all, but if you do be very cautious.