If one's charisma score is low, this obviously means that person is ugly. However, does the low charisma score mean that the person in question has an un-charismatic personality? I mean, can a person with a charisma score of 8 be ugly yet polite and charming? Rather than ugly while acting like a pig thug?

Charisma represents looks and personality, the latter much more so than the former. You should not have a lot of friends with only 8 Cha.

Charisma represents your character's strength of appearance, force of personality and ability to engender the sort of responses that they would like in other people.

With a low score, you may be so ugly as to make others not want to deal with you, be very shy or a recluse that is unused to dealing with others on any level, or so horrible in manner that you inadvertantly alienate everyone you deal with!

Or, all of the above.

People with low CHA will not be comely or alluring, however not everyone with high CHA is going to be physically attractive. They may just have a little something that the French call "J'ne se quois."

Yes, also, a person with low charisma generally has a less than stellar sense of self worth. 6-8 charisma characters should be insecure, directionless, and need the guidance of others to make their lives seem fullfilling and 'right'. For some reason this issue is very difficult for a few of our players to understand, however, it is my hope that if we keep hammering these responses out on the forums over and over and over and over and over and over and over everyone will benefit.