回复：为什么我听不懂老美同事说的笑话?

Same here. This means my English needs improvement. Not just the language itself, but also we need to know better to their culture. Sometimes I ask them why it is funny, they explain to me. I realize that in their jokes they quote a lot of roles/people/stories/words from movies, novels, and even news reports. If we don't know those kind of stuff, how could we enjoy their jokes? Of course there are some other reasons, but I personally feel this is one of the main reason.