I've been driving for over twenty years, in many different countries all over the world and I think that the standard of driving in Singapore is definitely the worst I have experienced.
1. Too many people drive whilst talking on the phone, smsing etc... it has been proven that even if you are using a hands-free device you are still as dangerous as a drunk driver.
2. Lack of anticipation. People rarely anticipate situations and are only reacting to what is directly in front of them. For example, when you see a lane closed sign, you will still see a lot of drivers keeping to that lane until the last minute, when they then have to push in to the next lane.
3. Signalling. Bad bad bad. People either indicate too early or don't indicate at all. I find that a lot of drivers are also very determined not to give way to someone who has indicated.
4. Taxis. I think the fact that they are driving all day is no excuse to drive badly. In fact, they should be the best drivers in the country given their time on the road but they are not that's for sure. Most of the accidents that I see on the roads involve a taxi, at least 90% I would say. Mirrors and indicators?? Not sure they actually need them in the taxi, I don't think they are used.
5. People generally drive too close, ignoring the two-second rule. I have been the victim of being hit from behind due to carelessness from the driver behind (and a taxi stopping suddenly to pick-up a passenger).