1) A type of statement or question that sounds or looks as though it is humorous, but is in fact, not in any way funny. Also called a non-entendre. Usually simply a reference, or a non-sequitur that is not even accidentally funny. Followed either by the phrase "get it?" or by immediate, raucous laughter if the audience are hipsters. (Hipsters are notorious for laughing at jokes they don't understand, to feign comprehension.)
2) A joke similar to 1., but with the intention of frustrating or confusing the audience, rather than pleasing them.
1) Bill: I drank so much milk I fell down, and I was like, whoa, what is this, Terminator 2?
(A minute of silence)
Mike: Bill, that's a lone, confusing reference, not a joke. It is also not a witty observation. You have now performed a hat trick of no-joke jokes, and unless you stop talking, we will throw you out of your own party.
2) An intentional No-Joke Joke:
Q: What is the difference between a duck?
A: One of it's legs are both the same!