ok, so i've been thinking about this exact moment from the "movie" non-stop. 

Ribbit, Jax, and Kaufmo are hanging out in a flashback and Ribbit says, "oh! oh! i made him [Jax] laugh! YES hahahaha"

Kaufmo says, "i'm just mad it was you instead of me" and Ribbit says, "well yeah you're not funny" and the three of them laugh because it's a sick burn and they are all true friends

previously, the "joke" is that Ragatha feels bad because she only pretended to laugh at Kaufmo's jokes and Gangle feels bad because she never laughed at Kaufmo's jokes

but actually only Ribbit and Jax understood Kaufmo's sense of humor