The term "smartens up" refers to the act of improving or enhancing the appearance, quality, or performance of something or someone. Some antonyms for "smartens up" include "dishevel", "neglect", "ruin", "mess up", and "deteriorate". Dishevel implies a lack of order, neatness, or tidiness. Neglect suggests a deliberate or unintentional failure to care for or maintain something. Ruin connotes the complete or irreversible destruction of something. Mess up implies a failure or mistake that results in disarray or confusion. Finally, deteriorate suggests a gradual decline or worsening of something's condition.