Bad drivers are those who don't know what is going on around them, who don't know the dimensions of their cars, who ignore stop signs, cut you off, try to squeeze over the curb, text/talk on the phone or get distracted and don't pay attention to the road in general. To give you an example of dangerous but not necessarily bad drivers - Jamaica. From my short experience there, the drivers constantly tailgaite each other, pass on the other side - but they do so in full control of the vehicle and they seem to know what to do in emergency situations. When tailgated, they pull to the side to let the guy behind them pass and when they see a car passing another car and driving head on towards them, they also know to pull to the side (well, duh) - instead of getting panicky and honking like crazy.

My definiton of 'bad' is not being in full control of the vehicle and doing stupid things like driving on the sidewalk, while by 'dangerous' I mean engaging in risky / aggressive driving behavior while still knowing your surroundings.