When I was younger, I had a friend who frequently expressed her hatred for the word "moist." It wasn't until the Internet that I understood this to be a commonly-despised word.
Oberlin College psychologists recently ran a study (read it here) to understand what about the word is so off-putting. From Nautilus:
People found "moist" most aversive when it follows an unrelated, pleasant word, such as "paradise." There seems to be a contrast effect going on here. "Moist" seems bad when following "paradise" but not when following a really negative word, like a racial slur. "Moist" also didn't seem so unpleasant when it followed words related to food, such as "cake." In contrast, it provoked the most negative reactions when preceded by overtly sexual words (use your imagination). These results show that reminding people of certain meanings of "moist" can affect one's disgust reaction to it.
Further analysis showed that "moist"-averse people also tend to dislike related words, such as "damp" and "wet," showing further support for the idea that it's the meaning, not the sound, of the word that's setting people off. "Moist"-averse people also tended to have more general disgust reactions to bodily functions, suggesting that it's the connotations with bodily functions and sex that sets people off.