1 rolling non stop at stop sign
eventually this will cause problems
2 driving too fast in residential or in parking lots
3 running yellows
like number 1 this common practice will cause an accident eventually
I have to disagree with #1 and #3, as I think they're minor problems. Certainly not top 3. Actually, in the case of the rolling stop, I don't think it's a problem at all! The goal of a stop sign is to ensure you check that the way is clear. The stop itself is not important.
My top 5:
1) Not being courteous - It covers so much, that it could be a top 5 by itself. It includes moving over for faster traffic, leaving space for merging vehicles, letting cars in from side streets when traffic is heavy, etc.
2) Failing to signal - Most people would think this is minor, but I think failing to signal is a big problem. Signalling is about notifying everyone around you about your intentions. I don't know about you, but I don't trust other drivers to figure out what I'm going to do without my signalling.
3) Tailgating - I am extremely aggressive at moving over for faster traffic. Even if such a move will mildly hold me up, I'll move over so I'm not holding up someone else. See #1. So if someone's tailgating ME, they're doing it wrong. Even worse if they have the chance to pass and fail to take it. What's the point of driving so dangerously close if you intend to drive the same speed anyway?
4) Not maintaining speed / braking unnecessarily - The latter is mostly a problem on freeways, as we tend to drive so close to each other that when you see brake lights, you almost automatically apply your own. This has an accordion effect down the line of cars and can cause some serious problems.
5) Speeding up when someone passes you - Seriously? Do you think I'm going to forget you were driving so slow just moments before and regret passing you because now you're riding my ass? Or was that a sad attempt at keeping me behind you?