In my case, I would say that I am mature enough to simply ignore this message and delete it as spam which is what such messages are supposed to be.
First you need to ask yourself a couple of questions: Why does this message exist? And what is its purpose? And answer is simple. To see response. It was important for sender to know your reaction. And for them there is nothing worse than usual ignore. If you start to ignore it right away, then usually fuse of such characters is only enough for a few messages, then they switch to someone else. But if you start to answer and succumb to provocations, then it will please them so much that they will stick like a leech, and even if you start ignoring them later, their persistence may turn out to be stronger and their fuse may last much longer than just a few messages.
As for your case, I don't even know. I doubt he'll be happy that you made him look like a fool to public. Maybe even threaten you. Anything can be expected from such characters. In Russia, we say about such people:-In still waters, devils will be found. So be careful.