Brilliant thread. An excuse to be grumpy. (Not that I need an excuse.)
People who pull up at night and leave their headlights on, particularly if they're on the nearside.
Bus lanes.
People who join the motorway, head for lane 2 and fall asleep.
I'll agree with others about the 40 in a 60 limit - particularly when they then come to a 30 and continue at 40.
Oh, and Simon Cowell.