He is noted for his ability to die and then show up again.
He enjoys mocking the status quo and refuses to adhere to the conventional sense of morality.
The Joker always stands outside established society.
He teaches us to see the sacred in what might normally be considered a mistake. He creates his own code of ethics. His motives are pure because he owes allegiance to no one. In medieval courts the fool was not an idiot. His value came from his isolation. Looking at society from his place outside the system, he was the only one who was able to see things as they really were. Court Jesters still exist and it is easy to recognize them. In a world of insincere masked sentiments, the trickster is the only one with enough courage to wear the mask of truth.
The Joker knows that laughter is the best medicine.
He wants you to laugh at yourself.
He is the part of ourselves that is still childish enough to be amazed at the wonders of the universe. He is not afraid to make a fool out of himself by attempting something new. Failure doesn’t bother him; the worst that could happen is that people would laugh at him and so what if they do? He is already a clown.
Wearing the Jokers image on your skin in any one of his many guises reminds you that the universe is scary, unpredictable, and uncontrollable. It also reminds you that miracles happen every day to the courageous few who dare to invite the Joker into their lives. After all, only the bravest among us will risk being called a fool.