People who don't indicate.
People who don't know how to use a circle.
People who don't give you space in bumper to bumper traffic (stupid I know, but I mean you're not moving so why not let me fit in?)
Troubleshooting IT issues with complete tools.
People who think they know more about your profession/field of work then you do.
Express tills in supermarkets that are in no way express.
People who switch from the slow lane to the fast lane and goes slower than the cars in the slow lane.
The Jack Russels downstairs.
Inconsiderate Neighbours who play loud music. Especially late at night in a (generally) peaceful complex.
Children in restaurants.
Parents who can't handle their children in restaurants.
People who take chances to get free food in restaurants by complaining about almost anything.
Taxi Drivers.

I think this might be a long ass list

But I'm overall a pretty patient guy.