It's a little known fact that to get by in life, one really only needs to know 237 facts. Of those 237 facts, you can actually get by on 236 of them, as the last fact, #237, is simply that you need only know the first 236 facts. So, in a matter of speaking, that is the 237th fact. Because this one is supplementary, I've included a bonus fact for today. Study it well as you're sure to need it in life.
The phrase "I don't give a damn" originally referred to an Indian coin called a "dam" valued at a 1600th (Some studies say it's a 64th or 40th, though the story's otherwise the same) of a rupee. It was literally the least amount of money one could give and was essentially worthless. Thus saying I don't give a dam is stating the thing in question has zero value.
Good people that we English speakers are, gave it that sweet old N at the end. So kids, feel free to express your distaste for something by using this expression. When you're parents scold, tell them you don't mean dam with an N.