Ad Hominem

Ad Hominem
Translated from Latin to English, "Ad Hominem" means "against the man" or "against the person."

Attacking the person instead of attacking his argument.
(For an excellent explanation of this technique, see Fallacy: Ad Hominem
A common form is an attack on sincerity.

A variation (related to Argument By Generalization) is to attack a whole class of people. (SARDINE MUNCHERS)

Another variation is attack by innuendo. Attacks don't have to be strong or direct. You can merely show disrespect, or cut down a person's stature by saying that he seems to be sweating a lot, or that he has forgotten what he said last week.  Some examples:

•  "I used to think that way when I was your age." 
• "You're new here, aren't you ?" 
• "You weren't breast fed as a child, were you ?"
• "What drives you to make such a statement ?" 
• "If you'd just listen.." 
• "You seem very emotional."

Sometimes the attack is on the other person's intelligence. For example,

• "If you weren't so stupid you would have no problem seeing my point of view." 
• "Even you should understand my next point."

Oddly, the stupidity attack is sometimes reversed. For example, dismissing a comment with "Well, you're just smarter than the rest of us." (In Britain, that might be put as "too clever by half".) This is Dismissal By Differentness. It is related to Not Invented Here and Changing The Subject.

Ad Hominem is not fallacious if the attack goes to the credibility of the argument. For instance, the argument may depend on its presenter's claim that he's an expert. (That is, the Ad Hominem is undermining an Argument From Authority.) Trial judges allow this category of attacks.

"The reason why an Ad Hominem (of any kind) is a fallacy is that the character, circumstances, or actions of a person do not (in most cases) have a bearing on the truth or falsity of the claim being made (or the quality of the argument being made)."