Select a cotton blue dress shirt. The Joker dresses very professionally, especially for someone with such sinister plans.
Put on a black or green tie. Cover the blue dress shirt with a green vest. Select a bright grass-green color that coordinates with the tie.
Add black pants, crazy-colored socks and black dress shoes. If you prefer to go even wilder, you can opt for purple pants.
Complete the outfit with a purple blazer. Shop secondhand or vintage stores for a bright purple color. The coat can be long and have tails or you can opt for a shorter jacket.
Spike your hair using gel. The Joker is known for his wild antics and hair, so the crazier the hair, the more you will look like the Joker.
This step is optional but it really makes a big difference for authenticity sake. In the actual movie, the Joker had massive scars around his mouth, lips and chin. Apply a prosthetic moth and chin or build up the scars using special costume makeup before applying the face paint.
Cover your entire face in white face makeup. The coverage can be spotty, almost looking as if part of the paint has worn off. Take a bright red lipstick and cover the lips and a large section around the lips. Take part of the red makeup and run it up along the sides of the face over the cheeks along the scar lines.
Finish out the look by using dark black makeup and lining the eyes in thick black strokes all the way around the lid. Add mascara to the lashes. The makeup should give the appearance that the eyes are sunken into the head. Complete the look by drinking a red-colored beverage that will temporarily stain the tongue and teeth red.
Finalize your outfit with purple or black leather gloves. A true villain can't be too careful and doesn't want to leave behind any fingerprints, so don't forget this finishing touch.