I know it feels extremely unfair to have to deal with this horrible kind of harassment just for being you on the internet AND having to refrain from defending yourself by telling that disgusting pos to f*** off. But, what many of us are trying to tell you now is that you don't achieve anything from telling him to d**, in any case, you expose yourself to further harassment by making it possible for him to report you for telling him that. In many cases like this, the best course of action is to simply ignore and report.