Players who can't stand to have a chink in their defenses, or a less than perfect offense. I call them "Cause-and-Effecters". Usually their method of operation goes something like this...
Last game I had to fight a Desolid bad guy...I'm spending all my points to make my attacks affect Desolid characters!
Last game, my Entangle was escaped from by a villian with Teleport...I'm spending all my experience to buy "Can't be escaped with Teleportation" for my Entangle!
Last game, I got hit with a Drain...I'm spending all my experience points on Power Defense!
These players are the hell bent on turning my RPG into a strategy game. They make me ill.
Of course, they're the reason that all experience point expenditures have to be discussed with me first. I love reminding them of their character concept, and how they must spend their points on things that fit within it!