For those unfamiliar with the concept, anti-jokes (also referred to as anti-humour) are similar to conventional jokes but the punchline is either missing or not what you would expect. You may argue that normal jokes, too, rely on punchlines you don't expect. That's exactly the point. You are expecting to be surprised by them (in a particular way). What a surprise when they're not surprising at all, or they are surprising in a different way. They tend to rationally explain something, taking whatever is being addressed in the joke literally, and they may turn out very dark. They're jokes that make fun of jokes. A joke-ception, if you will. Some people don't find them funny, some people do.

A horse walked into a bar. Several people got up and left as they spotted the potential danger in the situation.

Mary had a little lamb.

The doctor fainted.

Roses are red

Violets are blue

But roses can also be white

And violets should be purple.

Why was the turtle late for work?

Because he'd hung himself the night before.

What do you get when you cross a joke with a rhetorical question?

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Do you know any anti-jokes? Do you want to try coming up with your own?