We see Buggy naked after his clothes burn off from Crocodile setting him on fire.
A map to the One Piece is tattooed on his ass, but he isn't aware of this.
Crocodile orders Buggy to make a rubbing of his ass, and Buggy complies.
After getting the rubbing/map from Buggy, Crocodile prepares a crucifix to burn Buggy with, so no one else can find the map.
Mihawk saves Buggy, and states that, while Buggy himself is weak, his luck is extraordinary. Buggy is too important as a figurehead, and is a great motivational speaker.
Mihawk and Crocodile decide to train Buggy in combat skills and Haki, rather than kill him.
Mihawk: "It isn't wise... to kill former members of the Pirate King's Crew. Plenty of them still lurk. It would be one thing if we killed Buggy in a duel, but, if we betrayed our puppet of a colleague and slaughtered him in cold blood, I can think of at least one Red-Haired man who would be quite furious with us. I have no interest in angering a Yonkou, let alone an old rival."