Antonyms for the phrase "pretties up" can include words such as "uglifies", "messes up", "disfigures", "ruins", "spoils", "tarnishes", "defaces", "blemishes", "trashes", and "vandalizes". These words imply intentional or unintentional damage to the aesthetic appeal of something or someone, rather than enhancing or improving it. While one may attempt to make something or someone look more attractive, these antonyms suggest the opposite effect, leaving a negative impression or visual impact. It is important to be mindful of the language we use and the impact it may have on others.