Anyone ever have a character whose motivation for PC/NPC interaction was living hell for everyone in the party? This can be from any PC or NPC from games you've played.
I'll list a few personal motivations that come up often to start with.
1. The Assassin for Hire, or the "Murder hobo"
Seems to come up in every game now and again, you'll run across some hired gun sent to kill you at someone's expense or have a member of your party that does the same. It gets very upsetting when characters will be quick to kill any sort of roleplaying NPC with diamond jewelry, a +1 sword, and some fancy magic items equipped without talking to them first simply because they'll get more gold for their cause out of it.
2. The Troll, or "THAT DAMNED BARD/ILLUSIONIST"
Their motivation: To waste everyone's time whether it be bluffing out of convictions, creating duplicates of yourself, or stun/fascinate as many people as possible and just sit there while telling jokes or poking fun. Anyone whose ever played Part One of Rivers Run Red knows the feeling. It's frustrating to play against and its frustrating to DM.
3. The Instigator, or "Its never fun until someone gets hurt"
The character whose sole purpose in life it to create conflict in the most spectacular way possible. For instance, one character put all of their hard work into writing a book on poetry that took an entire year to perfect and shares it with everyone. Instigator reads it, says he's not impressed, burns it behind their backs, and makes it look like someone else did it. All adds up to a boring afternoon of complaints and fistfights.