Hair: Simon’s hair is pretty much a flattop with a small part in the front of it and the easiest way to achieve this is by going to a barber with a picture of him and actually requesting it.
You can also look for a “Flat top” wig at various stores and online if you do not want to alter your hair just to dress up like him.
Purchase a black or grey V-neck sweater. The lower the V-neck goes the better, because Simon has been known for having really low V-necks. This simple style can be found at many stores and are cheap at big box stores.
You do not have to alter anything on the V-neck; just simply wear it without wearing anything underneath.
Purchase some fake hair and apply it to your chest. Because Simon wears so many V-necks, you can see his protruding chest hair stick out and get commented on almost every episode of American Idol.
Place the hair so that some sticks out, and you can make it a little obnoxious unless you are going for a truly authentic look when creating the costume.
Wear normal pants, particularly black or tan khakis. Keep it simple like Simon does.
When you are in your costume, make it more authentic by learning to use a British accent. This way, you will sound and look like Simon does. Squint your eyes a little bit and judge people everywhere you go with rude comments.
Carry around a red Coca-Cola cup that is always featured at the judge’s table. This will help people recognize you more as an American Idol judge and is fun prop to have.