Some words, like this one kind of make me scratch my head. I would guess that an ultracrepidarian is someone unlikely to know the word "ultracrepidarian." In a somewhat related way, a person with a rhotacism is unlikely to be able to say, "rhotacism." The word "abbreviation" is long. The word "diarrhea" has been chosen by non-English speakers as a beautiful sounding word. There is an unintentional . . . not cruelty, but perhaps a contrariness in certain words where it makes me wonder why that word happened to be the one chosen for what it describes. I realize that these words are not connected in the same way or analogous to each other. I wish I had a word to describe what I'm trying to say!
I'm gonna tread dangerous waters here and say that some of them are ironic. As I understand it, irony is the defiance of expectation by contradiction. You'd expect "diarrhea" to be an ugly word, since it describes an ugly thing. You'd expect "rhotacism" to be pronouncable to people with a rhotacism, to describe their condition. Same with "lisp". Doesn't really apply to abbreviation or ultracrepidarian in the same way, so it's probably not the word you're looking for. It's a fun concept for a set of words, though