tickles you

The joke is basically a layered pun built on a very common phrase:

The normal expression is "That cracks me up," meaning "That makes me laugh."
The poster changes it to "That cracka cracka me up."
Instead of the verb "cracks," they use "cracka," a slang spelling of "cracker."
Because "cracka" sounds similar to "cracks," the sentence is still understandable, but it's grammatically wrong in a way that's intentionally silly.

The humor isn't that there's a deep meaning—it's that someone took a familiar idiom and broke it by replacing one word with a nearly identical-sounding slang term. It's the kind of absurd, low-effort wordplay that's common on meme forums: the joke is as much "I can't believe someone actually typed that" as the pun itself.

It has the same energy as saying:

"That pasta me off" instead of "That pissed me off."
"I'm cereal" instead of "I'm serious."
"Bone apple tea" instead of "Bon appétit."

It's funny because your brain instantly recognizes the original phrase while also stumbling over the ridiculous substitution.

"That cracka cracka me up." 😂
It's the kind of joke that gets funnier the longer you stare at it because it somehow manages to sound almost correct while being completely wrong. It has that classic internet-forum energy where someone invents a phrase on the spot and everyone immediately understands the assignment