Hippopotomonstrosesquipedaliophobia (3.5e Flaw)
From D&D Wiki
You have an irrational fear of "big words" (usually words with seven or more syllables or words that have a lengthy spelling (Constantinople, for instance)).
Effect: Whenever you hear a lengthy, intelligent-sounding utterance (DM's discretion) you must make a DC 10 will save or be shaken for two rounds.
Benefit: Bonus Feat
Normal: A character without this flaw is unaffected by large words.
Roleplaying Ideas: Characters with this flaw probably have a monosyllabic vocabulary, lest they say something that causes them to scare themselves. They also detest the name of their phobia, because it was probably made just to mess with them.