Being a "sucker" usually refers to being gullible or easily fooled. However, there are several antonyms to this phrase that convey the opposite meaning. Some of the antonyms for "being a sucker" include being shrewd, savvy, discerning, astute, and sharp. These terms are generally used to describe people who possess good judgment and are not easily fooled. Shrewd individuals are known for being clever and insightful, while savvy individuals are quick-witted and knowledgeable. People who are discerning are able to make wise choices based on careful evaluation and observation. Astute individuals are perceptive and have a sharp mind, while sharp individuals can quickly detect deception and avoid getting fooled.