"Be no slouch" is an idiom that means to be competent, skilled, or proficient at something. There are numerous synonyms that can be used to express this expression such as "excel," "shine," "prosper," "flourish," "thrive," or "achieve." All these synonyms imply that a person is not only good but has an exceptional ability to accomplish tasks with ease and expertise. "Be no slouch" is often used in a casual tone, but it can also be used in a professional setting to convey the message that someone is a talented individual who can produce excellent results. Overall, choosing to use one of these synonyms can add depth and precision to your writing or communication, allowing you to convey your intended message more accurately.