Two things:
People getting in the wrong lane at a roundabout.
People who don't use indicators, particularly at roundabouts.
( The Great Architect is still waiting for his account to be deleted on, Wed 17 Jun 2009, 12:37, archived)

GAH! No indicating is my biggest beef
Also tailgating when you're driving in the slow lane at 70mph and they have got 4 lanes to over take on. Same goes for people that try and squeeze in a queue at the last minute.
( Donkey Gums @mattcomedy, Wed 17 Jun 2009, 12:41, archived)

You mean on a motorway approaching a junction,
and someone has to force their way into the correct lane instead of being there in good time?

They piss me off more than most.
( Master Of Turnips. Only gays and morons believe in ghosts., Wed 17 Jun 2009, 12:43, archived)

Indeed, happens all the time towards hanger lane and bungs up the whole carriage way as no one can get past.
I've sat with my car revving fully and horn down constantly when someone did this to me.
( Donkey Gums @mattcomedy, Wed 17 Jun 2009, 12:45, archived)

You seem to have a inherent hatred for roundabouts
Come and live in basingstoke, kill or cure
Bonus fact:- Basingstoke is mentioned in the hitchhikers guide to the galaxy ref roundabouts.
( Gooch Is neither here nor there, Wed 17 Jun 2009, 12:43, archived)

This is one of mine.
I don't let people out if they're not indicating, even when it's obvious which way they want to go.
( Druid, Wed 17 Jun 2009, 12:55, archived)