Answer:
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.
