Cash machines that keep asking you if you want to see your balance. No, and I've already told you and I haven't changed my mind in the last three seconds.
People who say (for example) "Can I get cod and chips." I think this is another vile Americanism like "train station". Unless you plan to climb over the counter and secure the items yourself it's a daft construction. Maybe it's an attempt to avoid using the word "please" which some people seem to think adds an extra £1 to any bill.
People in supermarkets (usually women) who don't get their cash or card out until every aspect of the transaction is completed - as if they think stuff is free and doesn't need to be paid for.
People in supermarkets (usually women) who insist on discussing their cousin Flossie in Australia with the sales person even though there's a queue behind them waiting to put their stuff through the till.
Cunts (usually men) who ride their bikes down the pavement at 20 mph and imagine that you have eyes in the back of your head or radar so that you are aware of their (silent) approach.
The tedious twats who keep shoving adverts through my doors, 99% of which are for stuff I have no interest in. Why can't they just put it straight in the green bin and save me a job?
Ignorant twats in general, with whom this country is well supplied.