Anonymous troll
From dKosopedia
An anonymous troll is any person saying anything you find even slightly irritating, who does not instantly respond to your demand for their real name, SIN, home address and date of birth. Answering to such demands endangers anonymous trolls as a species.
So don't ask. If you find a troll especially irritating, answer with a recipe. The dKos TrollHouse Cookbook is composed of recipes that people threw at trolls who irritated them. This is a wiki best practice.