Oh, have I got a lovely word for you. It was voted Scotland's favorite word in 2007. It's dead useful, as Hagrid would say, because the world is absolutely full of people you can use this word to describe. It's pejorative, but it sounds affectionate, a combination I prefer because I don't like confrontation even a little bit. K thinks that it sounds like a word for "a whole lot," but that's not really what it means, although he's already talking about the numpty-nine times he's told Casey not to bark just today.
It has a certain charm, doesn't it?
I'm going to give you one of the definitions from the Urban Dictionary
because not only does it tell you how to spell the plural, it also gives
an illustrative sentence that makes me laugh (warning to The Easily
Offended: the illustrative sentence contains a Not Very Nice But Oh So
Evocative Word. You should probably cover your eyes.) So here's the definition, and all the rest: "Dialect, chiefly Scots. A bumbling fool or one who is intellectually challenged.
(plural : numpties) EX: 'They numpties couldnae organise a pissup in a brewery.'
In reference to members of Scottish parliament."
Apparently we share with our Scottish cousins the ignominy of being governed by a bunch of numpties.