When Randy Marsh has the world's biggest crap, the European Fecal Standards and Measurements Board, reveal that he was the previous holder of the title. Furious at someone beating him and making him "number 2", he proceeds to take a massive crap of his own, and beating out Randy. When Stan begins investigating Bono's odd behavior, its revealed that Bono did not take the world's biggest crap, but actually is world's biggest crap taken by a member of the EFSMB. He was transformed from crap into a human being when the board member fed him breast milk from his own chest.
This explained why he could do so much good and accomplish so many great things, and still appear as a piece of crap. Bono simply wanted to do so many accomplishes is probably so he won't needing to be "number two".
Bono later makes a appearance in 200 saying that the people of South Park had insulted him by claiming he was made of crap, implying that he denying the events that happened.