The phrase "icing on cake" refers to something that adds an extra layer of enjoyment or satisfaction to an already pleasant situation. However, there are many antonyms for this phrase, which represent the opposite of this experience. Some of these antonyms include "last straw," "final blow," "epitome of disappointment," and "nail in the coffin." These phrases convey a complete sense of despair, disappointment, and defeat. They represent the worst-case scenario wherein everything has gone wrong, and there is no hope for a positive outcome. Thus, while the phrase "icing on the cake" signifies excellence and delight, its antonyms represent negativity and unpleasantness.