Compulsive Truthteller (3.5e Trait)
From D&D Wiki
You cannot stand telling a lie.
Benefit: The fact that you are so trustworthy gives you a +4 bonus on Diplomacy checks and a +2 bonus on your Leadership score, if you have one.
Drawback: You have a -8 penalty on all Bluff checks, reflecting the fact that you find it nearly impossible to use words in these situations. You may attempt a DC 20 Will save in order to reduce this penalty to -4 at the time of Bluffing. This penalty does not apply on checks made to feint.
Special: One who is already a compulsive liar cannot take this flaw.
Roleplaying Ideas: "Did you and your comrades steal this ring?" boomed the voice of the guard. Gauler tried to eke a lie out of his brain, but he became nervous. "Yes," he said, hanging his head. Beside him, his companions shook their heads.