Bluetooth (especially people who wear their Bluetooth headsets even when they aren’t using their phones)
Instant Messenger (especially Yahoo IM, which causes this computer to crash and crash and crash. And then, just when you have reached the limit of your ability to cope, gives you the Blue Screen of Death)
The Department for Education and Skills
Local authority traffic management (which, incidentally, proves that Satan has a magnificent sense of irony. I always knew he wasn’t American.)
Those particular cyclists (not the well-behaved ones) who think that being on a bike makes them ethically superior and therefore exempt from the Highway Code and allowed to shout abuse at you for not swerving out of their way fast enough (I think that the law should make it legal to drive over cyclists when they are in the act of committing a road traffic offense.)
Local radio
Royal Mail Customer Services (More irony. Got to give him credit for that.)