I'm a problem player as well.
Impatience is what I consider to be my biggest fault. I get SOOO antsy and pissed off when I have to wait for people to take their turn. To the point where I actually timed people's turns for a session then presented my findings to the group the next day.
In retrospect, that was perhaps a smidgeon antagonistic.
But, TBH, nothing makes me want to paint my brains against the wall more than waiting five minutes for some wingnut to say, "oh, is it my turn?" Then I want to paint HIS brains all over the wall.
I also have a problem with loss of focus. If there's a bunch of stuff going on that isn't really relevant to what I perceive as the main point, I tend to try to push people to get going. "Yes, yes, it's all very well and good to discuss current politics with the greengrocer. Yes, YES, I know you're getting into your character. But, y'know, we are supposed to be saving those orphans locked up somewhere below Cauldron, so, could you please pull your head out of your vas deferens and GET GOING!"
:ahem:
I know what Dragonbait is saying.
"For some reason I have a difficult time really getting into other people's characters when I'm a player. I often really like my character, but am ambiguous about everyone else's."
Yeah. I'm guilty of that as well. Something I should work on. I remember we were about six months into an Eberron campaign and I still couldn't remember the name of one of the PC's. "Y'know, the dwarf cleric".

In my defense, I don't think the dwarf cleric once mentioned which god he worshipped and almost never spoke with a Scottish accent. How was I to know?