A few "rp hooks" that I've thought up but will likely never get the time to play out:

1. A non-stupid-race (read - not giant or duergar) PC who has some brain damage and will basically revert back to a childlike state when not engaged in physical combat. So for when you're pking/raiding/leveling/getting eq, you're Joe Normalguy. When you're trying to find a group, get inducted, buy things from a shopkeeper, you're a three-year-old. That doesn't mean you "always throw tantrums" or anything - you're like a regular three-year-old. Sometimes you're very sweet and endearing, sometimes you're easily distracted and slow to get something done, sometimes you're a whiny brat, and so on. Maybe during your cabal interview, you can't help but ask "Why" all the time.
Race: Something non-stupid (so people don't think you're just being a dumb fire giant or whatever).
Class: Doesn't matter. Probably not mage, definitely not invoker, unless you like pain, since I don't see an adult with a 3-year-old's mentality spamming spells much.
Align: Probably good/neutral (tough to play an inherently evil 3-year-old) but maybe that's another part of the hook - when you revert to child-like-ness you're not so much evil as you are normally.
Cabal: Doesn't matter - you can fit this role to really any cabal choice, though I think you'll have a hard time getting in to any cabal.

2. Try to speak only in song titles. Someone asks you if you want to group, and you reply with "Where are you going?" This role may not be visible to ANYONE but you while you're playing the char - but that doesn't mean it won't be fun. Especially when all is said and done and you reveal it - people might look back and go "So THAT is why he responded to my asking him if there were any hidden people in PK with 'I think we're alone now.'!"

3. Only speak in questions. 'Nuff said.

4. Asshole Assassin who full loots anyone he kills. Oh wait that's been done.