The phrase "bad apple" is often used to refer to a person, thing or situation that is not good or negative in some way. Synonyms for this phrase include the terms "rotten apple", "bad egg", "black sheep", "troublemaker", "villain", or "rogue". Each of these phrases suggests a negative connotation, implying that the person or thing in question is problematic or deviant. Other related terms include "liar", "cheat", "thief", and "criminal", which further emphasize the idea of wrongdoing or malfeasance. Ultimately, the use of these synonyms depends on the context and intended meaning of the phrase, but all convey the idea of something or someone negative or problematic.