Courtesy of reader M. T., here’s a graphic describing how not to conduct an
argument . . . er . . . debate . . . er . . . discussion. Yeah, that’s it: discussion. (Click the image for a larger view.)
The first, attacking the speaker rather than his/her argument, is frequently encountered on the Internet. Another useful link on that subject is Wikipedia’s list of fallacies. I’m sure many of us have been guilty of some of them from time to time.
Of course, XKCD has the last word on this subject: