From July 18, 2005 through June 2, 2008 he was rated by The Ring magazine as the number-one pound for pound boxer in the world. Mayweather has won six world boxing championships in five different weight classes; he is the former WBC welterweight champion, a title he vacated upon his retirement. He was named Ring Magazine Fighter of the Year in 1998 and 2007. He is currently ranked number 2 pound for pound fighter.
Now for the facts:
He ended up being a pussy and declined from fighting Manny Pacquiao. So, he has created "fail expectations" for nearly 80% of the world awaiting this bout.
The term is used for relating to high expectations that diminished immediately.