Introversion (3.5e Trait)
From D&D Wiki
You find pleasure in spending hours alone, but, in result, not at all comfortable when in large groups.
Benefit: You gain a +1 bonus to Charisma-based checks when dealing with one creature.
Drawback: You suffer a -2 penalty to Charisma-based checks when dealing with more than one creature.
Special: Cannot have the Extroversion trait.
Roleplaying Ideas: Some characters are never really able to stand large crowds and are usually the killjoy of any celebration. They are often percieved as shy or to be loners when in reality they just prefer to have time alone. They rarely speaks, for one of many possible reasons, but most often because they don't feel like talking. Though they may not be charming as the outgoing ranger or the creative bard, they harness an intellect that few are aware of. Your character might despise people in general and may only stay with people who are under her control.