By far, the funniest dictionary gaff I've ever heard came from one that everyone had at a company I worked for which, I think, WAS one from Merriam Webster! It was a generic, small, red paperback type that most offices gave to their employees back then (mid-80's).
Someone told a joke which, literally, could have been this one: "How do you circumcise a shark? Four skin-divers! (Foreskin divers!)" There was a guy who's primary language wasn't English listening and he grabs the dictionary to look up one of the words. He finds one, then flips the pages to another, then flips back and looks up puzzled. Turns out, all the dictionary had as the definition for "foreskin" was "The prepuce." and all it had as the definition for "prepuce" was "The foreskin." Hilarious!
With that kind of logic all you need to do is make up two words that point to each other to get into the dictionary.
"Bapu" --> "Unfunny"
"Unfunny" --> "Bapu"
See? ?