Not everyone can wear crazy shirts that can truly be called crazy. That's why you need to find crazy shirts from a website that understands what it means to be crazy.
First of all, you won't find the crazy shirts at the store or at a regular store. Those stores have the ridiculous t-shirts that everyone else has been wearing for months. That's not cool. You need to find a source for crazy shirts that feature designs that no one else has. You need a find a website with crazy shirts that emails you the second a new design is available. You just can't get that sort of service from a major department store.
You should also find a place that isn't afraid to be controversial or offensive. Being crazy means not being worried about what other people think. At the same time, being crazy means knowing the difference between being funny, and just being obnoxious and crude. Remember, being crazy isn't for everyone. It takes wit and good taste and vision.