In three experiments, researchers from Oberlin University in Ohio and Trinity University in San Antonio found that more than 20 percent of participants where averse to the word.
Again, why? Not the sound, apparently, but its association with bodily functions. The younger and more neurotic the study participants were, the more likely they were to dislike the word. Additionally, the more disgust they associated with bodily functions, the less they liked moist.
When I was buying romance fiction for Woman's World, someone once sent a story with the immortal line "It only served to wet my appetite, which was already damp."