Anyone who has lived with cats can testify that their sense of humor tends toward practical joking. They don't have the kind of facial features that allow for smiling--purring serves that purpose. Cats also don't laugh out loud, but when a cat executes a prank successfully, it always seems pretty pleased about it.
Some cat jokes are part of their play and mock hunting activities. Popular with kittens is the secret stalking and Sudden Ambush of another kitten, older cat, human, well basically anything. Adult cats also will sometimes play this game with each other or with humans. If the cat about to be ambushed, the Stalkee, hears or catches sight of the Stalker, the cat being stalked may sit up and make eye contact with the Stalker as if to say, "Oh, no you don't!" That round is chalked up to the Stalkee cat who would have been ambushed if it hadn't been alert.
Some ever-popular jokes that cats play include-
Sudden Pouncing From Nowhere.
Batting at the other cat's rear end when its back is turned.
And slow-motion invasion of territory.
An example of the slow motion invasion, is the cat lying on a pillow with the human and gradually "cuddling" closer to take more and more of the pillow until the human is nearly forced off of it. From the cat's point of view this joke is also a matter of expanding its territory, at least in the short run. If the human tries to take back the pillow, the cat may protest vocally, as if to say, "Hey that's my space now!"
Much of cats' play has to do with their finely tuned sense of pouncing range. I once knew an elderly female cat who lived in a household with a very aggressive macaw. Those birds have powerful beaks, and the macaw was bigger than the cat. The cat could easily have been injured or killed if the bird ever got close enough to bite her. It never did.
When the bird was out of its cage, the cat stayed prudently out of reach. But the cat observed that the bird could only lunge so far through the bars once it was in the cage, so she stationed herself about an inch out of beak range. It drove the bird crazy, and it never gave up trying to get at the cat. But the cat was serene. If that cat was laughing, it was very quietly to herself.
This is Spaz sleeping. he's a good cat. :D 
This is Piper! No, it's not a boy. My sister wanted a girl cat, oh well! 
