Many courts no longer enforce dress codes, but that does not mean that you should dress disrespectfully. Wearing clothes covered in profanity before a person who has the power to put you in jail is never a good idea. Show that you understand the seriousness of the occasion by dressing appropriately for court.
Now I do believe in freedom of speech and free self-expression. But is it any wonder that a woman wearing a shirt emblazoned with the words, "COPS LIE," found herself arrested when she violated her probation?
