Some of my faves are local ones from the North of England. I love apeth - most frequently collocated as “you daft apeth” which I guess is calling someone as stupid as an ape with an old-fashioned dialect affectation. Another one is piecan which has a similar meaning - you are as stupid and dull as a metal tin which holds pastry.
I’m also a fan of twerp, and the etymology of that - Tolkien? American dwarves? Racing pigeons? - is intriguing.
Otherwise, to travel-sourced insults, Italians are great with curses! As far as I understand, the word terrone is roughly equivalent to ‘redneck’. Used to slag off Southern Italians, it carries all those cultural connotations of someone being slobby, uncivilised, lazy and so on.
Meanwhile in Rome, mortacci tua - or 'tacci tua - is pretty much a curse on your ancestors, though it can be friendly! It depends on context and as far as I understand it’s a very Roman way of saying “your Mum”. Yeah, it’s probably safer just to call someone a piecan…