Vermis - as I like to say, beware the Berk in the Merc...
Personally, I drive to the speed limit and conditions - I want to get where I'm going, but equally, I want my car, my driving license and especially my life tomorrow. But there's been plenty of occasions where I've had to slow down, to give myself space to the car in front, because some moron's come right up behind me and has no way of stopping in time if I have to brake suddenly.
But they're minor compared to some - every time I think I've seen it all whilst driving, someone goes out and achieves a new world record for idiocy.
For instance, the other day, I was taking a different route into work (there was an event on which clogs traffic up for miles around), which takes me past an infant school, which is on a narrow country road, where the parents park on one side (which was the side for the direction is was going), so you have to hop the spaces to allow traffic coming the other way to get past, else it's gridlock (and is the main reason I don't go that way normally).
I managed to get enough space to hop into a gap, but I couldn't get further without blocking off oncoming traffic, pulled in, put the handbrake on, and watched the car behind me go sailing past, all the way down to where traffic was queuing and oncoming traffic was just about to come through. Cue people having to go up the kerb just to get past this dimwit.
Also, there's a roundabout on the way home from work that has a garage and a mini roundabout fairly close that causes traffic to stack back onto the main roaundabout, and if someone doesn't come all the way around on the inside and then try and jump in the queue at the exit at least once a week it's unusual. I almost want to ask them if they're carrying an organ for transplant or a pregnant woman who needs to go to hospital now, and when they say no to both, tell them they can queue up like everyone else then.
I've even been overtaken on a mini-roundabout near my home - it's at a t-junction to a motorway sliproad, I was going straight on and was in the correct lane, some woman in a small people carrier went into the other lane as though she was going to go down the motorway, then dived straight in front of me.