How to look evil....

First grow a goatee.  This is especially imperative if you are going to be an evil twin.  

Also, you should take note your the color of your clothes.  Robin's egg blue does not make you look evil, rather it makes you look just silly.  However a dark grey shirt will do the trick.  A general rule of thumb is to go with dark colors.  It is also helpful if the shirt is tight and form fitting, something on the order of what a typical douche bag would wear to a club on a Friday night.