When someone is caught committing a crime (mainly one sexual in nature, but can refer to all crimes), with overwhelming evidence to prove they did it; in their defense, the culprit denies that they were the one caught doing the crime.
Derived from the Shaggy song "It Wasn't Me", which describes a man being caught having sex with another woman by his wife, and subsequently denying that it was him she actually saw.
When caught on video having sex with a 14 year old girl, R. Kelly employed the Shaggy Defense; he just denied that he was the one in the video.
The ultimate being, he is the one who has the divine power of god. He can only use 1% of his power because if he uses his full power, the earth will be destroyed by his pure raw power. Even when he only uses 1% of his power he still kills any foolish mortals in his area.
Fred : We can only film with shaggy for 5 seconds at a time, if we try to film more than that. The entire set will be destroyed and every living person will be shredded to pieces.