I dislike the name Dumbtionary. A person isn't dumb just because they can't spell a long word.

Author Donald Westlake once wrote a book with a bunch of apprentice gangsters whose speech epitomized the stupid. I'm going to paraphrase the way they talked.

"One thing Mikey taught them was that if some fucker came up to them and talked about some fucking great idea he had, that they should back off and first ask "What the fuck?"

In my opinion, that's the typical speech of stupid people.