BRITISH PHRASES
Dog's dinner - If you make a real mess of something it might be described as a real dog's dinner. A bit like some joint Anglo-American approaches to Eastern Europe for example!
Donkey's years - Someone said to me the other day that they hadn't seen me for donkey's years. It means they hadn't seen me for ages.
Drop a clanger - When I asked a large lady on the tube if she would like my seat since she was so obviously pregnant, she took the seat then told me she was fat, not pregnant! Boy did I drop a clanger. You might make a gaffe. Either way it was horrendously embarrassing, especially as half the people on the tube had heard me!
Duck - In and around Leeds you will find older people might call you "duck" in the same way that they might call you "love" or "dear" in other places. Usually pronounced more like "dook", which rhymes with "book".
Duff - Anything that is duff is useless, junk, trash. It usually means that the object doesn't do the job it was intended for. Our last Prime Minister was pretty duff!