The phrase "wears threadbare" implies that something has become worn out or overused due to excessive wear and tear. Synonyms for this phrase can include "tattered" or "frayed," which indicate that something has numerous tears or worn spots on its surface. "Shabby" is another useful synonym that suggests something is worn down or in disrepair. Additionally, "worn" or "faded" can convey a sense of weariness or exhaustion with continued use. Ultimately, any synonym that conveys the idea of being worn or used up can effectively replace the phrase "wears threadbare".