A good word to describe someone who is overly complimentary to someone about something is "flatterer." A flatterer is someone who excessively praises or compliments others in an insincere or ingratiating manner, often with the intention of gaining favor or advantage. Another term that can be used is "sycophant," which refers to a person who seeks to gain favor or advance their own interests by flattering or fawning over others. Both words imply that the compliments or praise may not be genuine and are used as a means to an end rather than reflecting true admiration or appreciation.