There are times when you will not be able to explain anything to any of your friends, if they do not recognize the first Noble Truth, that Dukkha exists. If people don't want to recognize that, and especially if they don't want to recognize the second Noble Truth. "Lot's of it comes from here, friend." If they do not want to recognize that, then your not going to be able to explain to them that indulging sensual pleasure will lead to Dukkha. It's just that simple, because they won't believe it.
If they have had Dukkha, if they accept the Dukkha was there, and it was too big for them to work with, and they are interested to know why, how, what, and so on, then you might be able to explain to them a bit of the practice. But quite frankly, I wouldn't start using the word Dukkha in your first sentence. And it is true, many times it is just caring and not caring. Most people are just not open, they are not ready yet. But when you think of not ready yet, where were you ten years ago, fifteen years ago, twenty years ago? I know where I was when I was nineteen, and I was not ready yet. So maybe your friend will be ready next year.