I believe that funny teachers are often the teachers who truly love their subject. These teachers make their lessons fun, and their classes fun to be in. That can be a lifesaver when a student just doesn’t want to be there, or is having a bad day. The light humor makes a classroom comfortable, and learning easier.
My AP History teacher senior year of high school made learning American History so much fun, I regularly watch the history channel and “American Experience” tv show now. When we were learning about the sixties, and hippies, he made us all come in to school dressed as hippies. We then went and protested against another teacher’s class. This teacher had directed everyone to dress up and dress in military garb. The teacher was a former military general, and usually very serious, but everyone had fun that day as we recreated one of the protests that usually went on. Sure, we burned a day of class and had fun, but I always remember it. He always did little activities or had running jokes that made the time pass, and made me remember and retain the material.