I teach adult students and they always have difficulty expressing what they want to say, no matter how advanced their vocabulary is. I downloaded short jokes from the Internet, cut them into strips, and distribute them randomly. The goal is to express the short joke in their own words, without reading or memorizing. Be sure to model how a person tells a joke (like telling a story, with facial expressions or everything). You might need to help them with understanding some jokes, as some are contextual/cultural.