Just came across this great site: www.urbandictionary.com
I like "fucktard". Noun: A contraction of "fucking retard".
I called one of the blokes in The Bar "dunderfuck" once. It really really works for him. He's a blundering idiot with a great sense of self-importance, and the look of someone who reads Harry Potter and asks for "A pint of your finest ale, sire" in country pubs. Now you know about him, see if you can spot which bloke I mean.
Of course, it wasn't to his face, so don't go up to him and say, "Hey! Are you Dunderfuck?" or anything.