Some of you have asked me why I used that term "cool muthafukca". I got it from the movie "Pulp Fiction" , where Samuel L. Jackson -- in a classic performance -- ask for his wallet, the one called "Bad Mother Fucker". Well, I didn't want to use that exact term so I altered it.
The point is that Phelps is a cool person in and out of the water. In the water, he cooly destroys the competition. Out of the water, he's a cool person to meet.