Mine has got to be people who do not bother indicating, especially when on the motorway and you see someone who is speeding past and then suddenly cuts right infront of you causing you to slam the brakes on and of course, they never indicated either.
Another new one which reminds me of what happened last night, was waiting at a T junction and the last car that came and turned into to where I was waiting turning out of, the driver finds it amusing that I am the one having to wait at the junction and he has the right of way first. He looked at me, smirked and laughed just as he turned into the road. Complete plonker.
Also people who think that it's ok to cut you up on a big roundabout without realising that there is a car behind them because they want to quickly turn off at the exit that they were heading for and without indicating either.
Oh yeah and lastly, people who turn into roads and cut right into the opposite side of the road first instead of going around the T junction give way painted in the middle of T junctions.
Liam