I am a problem player in a couple of different ways:
1) I will be the first to admit that I am slow to take my turns. The first part of it is that I am naturally indecisive, so it takes me a while to make tactical decisions. The second part of the problem is that I need a pocket calculator to do basic arithmetic, so it can take me a while to add up my dice from a damage roll. At least I am attentive and always know when it is my turn.
2) I am bad with names. Not PC or NPC names, but people's names. I can play a D&D game with the same people every other week for a couple of months, then turn around and have to ask one of them: "err, what was your name again?"

Yet, I can remember their PC's name just fine! I need better people skills.
3) I am a bit of a minmaxer. When I first read the Alternity core rulebook from so that I could learn the rules and make my first character, I discovered that while most gun skills were based on Dexterity, heavy weapons were based on Strength. So I used Dex as a dump stat and created a powered armor equipped soldier specializing in Machine Guns, Rocket Launchers, and Melee Weapons, yet who couldn't hit the broad side of a barn with a handgun.
4) My characters are also often rather unimaginative. The character mentioned above felt like a square peg in a round hole since he was a pretty typical soldier-type in a campaign full of crazy and imaginative characters with a ton of personality and unusual quirks. Later on, when my own brother was DMing a 3.5E D&D campaign and asked all of the players to come up with personalities and backgrounds, I don't think he was very happy with mine. My characters often end up looking like slim excuses for various class/race/ability combinations. I am working on this one though!