But I want a gismu to exist that's intentionally "rude"
A word (in probably any language) is considered rude when it is a taboo -
if the speakers of that particular language are conditioned NOT to say it.
From kindergarten to highschool or whatever exists in Your culture You're
told You mustn't ever use those malvla. In contradiction with all that when
You're feeling unbearable anger You do utter those forbidden words. That's
why they have effect - they calm You down in a relatively short time.
Assume there's a gismu, say, {babca}; do You find it offensive? No, because
it is not something like "F*ck a donkey etc.", it is artificial and meaningless.
Offensive or rude words are always metaphors.
IMHO there's no use of creating such a word.
mi'e xiLI,odor.