The Troll — Everyone knows this guy (and it’s usually a guy), who intentionally visits sites in order to stir things up, provoke a furious reaction from other posters and then disappear. Classic examples are the Free Republic types who visit Daily Kos and vice versa.

The Skimmer — The commenter, usually sour, who reads only a headline or sentence of a piece, draws exactly the wrong conclusion, and then embarks on an embarrassing rant.

The Kumbaya — These folks always show up two-thirds of the way through any heated on-line debate and ask, “Why can’t we all just get along?” They are inevitably ignored or trashed.

The Parser — What would we do without the Internet Grammar Police? These folks assiduously correct the online writings of others — never quite catching on that the Web is designed to be fast, fresh and sloppy.