Japanese comedy gets a bad rap. Foreigners either knock it for being too silly and too focused on slapstick or too pun-based and difficult to understand.
The Japanese sense of humor is most definitely different from its Anglophone counterparts. Some things, however, are so funny that they transcend national borders and linguistic barriers. Learn the next few phrases, and you'll soon be laughing it up in Japanese.
It's funny to catch people who aren't paying attention. If, for example, a group of friends are having a conversation, and Stan, an affable guy with a paunch and a tendency to daydream, ends up staring off into the distance, the rest of the group can laugh at him when he finally comes back to reality. In English we use NASA-style lingo to try and "contact" people like this who have "spaced out" — "Earth to Stan. This is Earth. Do you copy? Come in Stan!"