As an alternative: I played a character with very similar stats a few months ago, and the direction I went was that he tried very hard to be pleasant and charming, but always ended up accidentally threatening or insulting everyone, not just the people he tried to intimidate. This was usually by calling attention to his physical prowess at inappropriate times, but sometimes he was just uncomfortably blunt.
As an example, the party was once foolish enough to let him be the one to make first contact with a little girl we found crying in the attic of a haunted house. His opening line was "Hi there, I'm Michael. My friends and I probably aren't here to kill you." In his head, we weren't there to hurt her, but she might turn out to secretly be an evil ghost (she was) and it was important to cover all the possibilities.
He was smart enough to know that he had a problem, but he still felt that he should try to be polite and friendly and never noticed his slip-ups until it was too late.