I posted this on my Facebook (*eye roll*) but I'm posting it here for posterity's sake.
In face to face conversations, people will use these tactics but somehow usually manage to have a little more tact about it. On the internet, however, forget about it. Anonymity and the opportunity to experience other people as textual blurbs on a personal computer screen give one near absolute permission to behave like a tremendous dickwad.
This lovely satirical piece (which is also dead serious) outlines how you, too, can marginalize and insult practically anyone!
Derailing for Dummies