I've had my fair share of troubled employees, most of which were just angry because the world didn't revolve around them.
Probably the worst employee I have ever had was terminated about a month ago after I caught him stealing.
He was the type of employee that always seemed to have a chip on his shoulder. He was OK when he was first hired, although he always had a defiant attitude and seemed to think he was above having to do part-time work. Then he got injured. He claimed (and I say claimed because no one witnessed this happen) that he permanently injured his knee when a package hit the back of his leg while he was working a pick-off position. Multiple doctors said nothing was wrong with his knee, and the doctors who thought it could have been injured said it couldn't have happened the way he described. Either way his insurance claim was denied and when he came back to work he claimed that UPS management was the reason his insurance claim was denied (we have nothing to do with it).
When he came back his attitude was the worst I have ever dealt with. He was working a pull and park position and he would walk as slow as possible and drive only as fast as the truck would idle everywhere claiming he was working "as fast as he felt safe". Obviously we couldn't do anything about it because you cannot discipline on performance. We suspected him of stealing, but could never prove it. There was even a case where a package containing 50lbs of marijuana went missing from the center manager's office (it was being held for DEA seizure). When we finally located the package it was sitting under a trailer in the yard and we witnessed him drive his personal vehicle up to the trailer, got out and looked around, saw us watching him, got back into his truck, and left. When security pulled him in for an interview he of course denied everything.
A few weeks later a p/t sup found a brand new golf club hidden in the shadows beside the building. We decided to leave it there and stake it out to see who came back to pick it up. Sure enough, at midnight (about 2 hours after the shift ended and everyone had gone home) seconds after the last feeder driver left the yard, this employee pulls up and grabs the golf club. Myself and another sup come out of the building after watching him grab the club and confronted him. The look on his face, knowing we had just caught him red handed doing what he had so adamantly denied, was worth all the grief he had caused us for the previous few months.