I love teaching visual irony & humor in art. I usually introduce the idea with a lesson where students have to place a snow person in a situation they could never find themselves.
We then look at the work of Gary Larson (The Far Side). Students have to come up with their own comic that uses visual irony. I encourage them to pull in what they are learning in science/social studies/math to their work. I usually do this with 4th Grade.