There is no "right" or "wrong" as a constant (at least that is how you have to see it) but in the context of your community, your society and the civilization that you live in, there is a "right or wrong"
You can argue from a an ideological blank, by implying that it is will, and personal perspective that dictates this, but you can also follow this up with the fact that the world that we live in, and the comforts they're capable of enjoying (be it promiscuity, or drug use) is only possible because of social will putting rules in place that allow them to enjoy it without being destroyed by the absolutely willful.
You tell them that, by embracing the shades of grey, they're absolute pieces of shit, and you prove it to them by taking advantage of their weakness, call them out on it, and if all they can manage to drum up is a "eehh, I don't care man, #YOLO" then they're a lost cause and absolutely untrustworthy.
You cannot depend on them, they lack will in any meaningful sense and have chosen nihilism-lite as a means of rationalizing their own weakness, if the time comes when and if they need your help, be it for something benign or serious, then leave them to their own devices, keep those kinds of people at arms length.
Now, Nietzsche's philosophy doesn't outright call for the destruction of ideals or morality, it more or less implies that if one system isn't working, you simply build one that does from the ground up. It should be used as essentially a spiritual palette cleanser for more relevant forms of "right" and "wrong"
the tldr; is pretty much this.
These people are fucking useless, and you can't really argue with the truly depraved, since they jump to the logical conclusion, and that's "Yo man, we're just a shit on a shit speck, nothing matters"