Kellogg recently dropped olympic swimmer michael as a celebrity endorser. kellogg's decision was based on conflict of interest with another sponsor a contract dispute the age of the celebrity negative behavior involving the celebrity overexposure of the celebrity

negative behavior involving the celebrity

Explanation:

The negative behavior that conducted by a brand representative tend to resulted in negative consumers attitude toward the brand itself.

At that time,  Micheal Phelps were caught in a photograph while smoking marijuana type (this happened in 2009, at that time it's considered to be extremely taboo for athletes to do this).

To avoid negative press, Kellogg decided to dropped Phelps and choose other people to endorse its product.