Co-workers who withhold information that you NEED until either (a) the last minute or (b) you think to ask them about it, in the name of playing games, rather than producing the best possible work product?
If I didn't know better, I'd think we worked in the same place :-)

If I were a boss, I'd fire anyone that did this. In fact, I once had a boss who more or less did this. He was a crap manager, but he suspended an employee who withheld information to screw over a fellow worker because in doing so she screwed him over too. I love the smell of karma in the morning.