Life - In reality, nothing is funnier than true stories. When we occasionally share personal stories that are funny, we can help the students see an instructor multi-dimensionally. For example, if you are presenting the concept of momentum, throw an egg at a sheet held up by two students. This is active learning. Have some fun with some of those terms.
Good wordplays can be a lot of pun.
Play the part. Humor should be appropriate to the situation, personable, and it should contain something of the personality of the instructor. Learning is much too important to be taken too seriously. Making fun of someone is not good humor. Humor at the expense of someone in the class is dangerous.