My agency had an employee who was known for playing with his gun at his desk. One day he had an accidental discharge, and he got fired. His appeal went on for 12 years and he won. He was reinstated with full back pay. At that point all he had to do was hang out for two more years without screwing up and then retire. BANG! Another AD, and he was fired again. That time it stuck because he had signed a special form as a condition of rehire that any more AD's would result in termination.
One of the problems with making firings stick is that the ratings system in government service is completely ineffective. It is made to make everybody look great, regardless of performance. It also makes an effective defense when appealing termination because people pull out their ratings and say "Look, I was an effective employee who just made a mistake."
So he was fired four times. (grin)