I was forced to train someone so cocky that they ended up doing a rm -rf / on our production server a month after I quit. He also accidentally euthanized a legacy server, deleted the accounting database when he was trying to do a hardware based RAID rebuild, completely destroyed the Windows domain server and mocked my daily tape backup regimen - opting to ship USB consumer grade hard drives in an unpadded steel box instead to off-site storage... The list goes on. He literally destroyed everything he touched. The only reason he wasn't fired was because he was a pretty man.