The man who speaks to you this week used to be a baker, and he never liked to give his customers a "baker's dozen" when they bought twelve. He told them thirteen is an unlucky number.
The man tells the story of a jury he was on. As was often the case with him, he had a hangover and doesn't remember the beginning of the trial. After a while, he notices there are thirteen jurors instead of the regular twelve. The thirteenth juror is invisible to most of the court. Only the man who tells the story knows that there are thirteen there... and one other man in the room has a strange feeling that there's one too many jurors.
Is thirteen an unlucky number? Perhaps, for the thirteenth juror.
"It was only when he had a drink that he was bad..."