Jose Canseco, the former baseball player, shot himself in the hand recently. Story here.
He didn't accidentally shoot himself; he negligently shot himself. Firearms do not 'accidentally' discharge unless they are defective and have a mechanical malfunction.
He failed to observe proper firearm safety procedures and did not unload the weapon. When cleaning a weapon, the first thing one should do is unload the weapon (visually verifying the chamber or cylinder is unloaded) and remove the ammo from the room or immediate area. Hands or body parts (or anything living or of value) should not stray in front of the muzzle. Had Mr. Canseco unloaded his weapon and handled it properly, this would not have happened.
"Gun cleaning" is often a euphemism for improper handling, though we don't know the actual details here. This is why guns must be handled with respect and the safety rules observed at all times by everyone.