Definitely feeling your Swan Taxi pain JoshE, generally they see that one guy in the group with long hair and decide he's going to stab them!
I also can't stand people who don't know who to merge - if the left lane is ending fucking indicate, and the person in front has right of way!
Also agree with everyone else who has mentioned slow walkers, for this reason I can't stand shopping centres or tourist areas.
Discrimination is probably one of my biggest issues though, I really hate seeing minority groups lose opportunities and have their lives made harder by sheltered, middle class mediocrity.