It's our stereotype of English cooking.
Hell, it's Britannica's, too. See this recipe for boiled beef and carrots, "a truly traditional Cockney dish."
http://www.britannia.com/cooking/recipes/boiledbeef.html
The meta description for this says "Explore and discover the joys of English cooking."
When you have to go to a reference source to explain a slur, it's just not working. So I guess I have no recourse but friendliness. Welcome.
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What others say about boorite!