Antonyms for the word "prettying up" include words that convey the opposite meaning, such as "uglifying," "disfiguring," and "vandalizing." While "prettying up" suggests improving or enhancing the appearance of something, antonyms imply a negative impact on its aesthetics. "Uglifying" implies making something visually unappealing or unsightly, while "disfiguring" suggests causing damage that alters its original form. "Vandalizing" means intentionally destroying or defacing something, which can result in a loss of its beauty. So while "prettying up" is a positive action, its antonyms signal the opposite, which can have detrimental consequences.