From Dictionary.com:

–adjective
1. appealing to one’s prejudices, emotions, or special interests rather than to one’s intellect or reason.
2. attacking an opponent’s character rather than answering his argument.

I guess it is a part of human nature to engage in ad hominem attacks. It seems to be so easy to argue a point by just discrediting the other debater. it takes the focus off your position and on the messenger of the other argument. It truly is small minded though.

If you are trying to persuade someone then persuade them. Appealing to their prejudices is juvenile at best. It is obvious that your argument can not stand up on its own. Usually ad hominem attacks are caused because people are insecure about their ability to make a valid point.

Next time you find yourself focusing on the person’s past problems or appearance remember that you are not judging the merits of the discussion, which an intelligent person should do, but rather just being led away from the topic.