I know a joke in baby language. It's "abbu, babbu." I don't know what it means, but every time I say it to my daughter, she smiles really big, and sometimes laughs.
I know it's funnier than other things I say, because normally when I try to replicate her baby babbling (made more difficult because I am now just an english speaker, while she is still able to learn any language, thus can make more sounds), she just looks at me, or talks to me some more.
But abbu, babbu, that's some funny stuff.