That's Yucky! is an expression used to express disgust or disapproval. It is often used when someone finds something unpleasant or unappealing. UGH, GROSS, and EEW are all words that can be used to express this sentiment. UGH is a sound of disgust, GROSS is an adjective meaning disgusting or repulsive, and EEW is an exclamation of disgust. All three words can be used to express the sentiment of That's Yucky!