Blunt infers a hard surface like a hammer. So rather than discuss a subject as if you were using a fine scalpel you use instead a heavy steel hammer.
So I might say gently to my wife, "when you point out my imperfections a little bit of my love dies for you" or " I HATE YOU" the second is being blunt. :-) and is, of course, not true.
Do we use this much in the UK? No, we are a small island with many people so subtlety is the name of the game here, as you can imagine this irritates many Americans who just want to "say it like it is" and we look shocked.