Also the place where I live - a small suburb of Dublin, Ireland. The name itself is an anglicisation - from "Domhnach Broc" - The Church of St. Broc in Irish. It came to mean fight or brawl for the reputation gained by the Donnybrook Fair which ran there from about 1204. I've never heard it used seriously, but I'm told it's common enough in Australia. See my writeup on the fair from more info.