Cockwomble is an interesting and modern insult. It's somehow not too offensive, yet funny in equal measure.
Phlegm.....beautiful word, sounds like what it is. It couldn't be something nice like a cream cake, could it? "I'll have two stotties and a phlegm....." Why isn't it spelt flem....imagine a foreigner trying to pronounce phlegm.........phleggum
Double-Dutch......for sure. Why do foreigners say 'for sure'? I haven't heard one Britisher say it. Ever.
Dick-spasm is my personal favorite insult and word, although I'm not sure it is recognized by the E.O.D....