Usually I am a positive person, but sometimes it is fun to get a bad attitude. And when you do, why not wear it on your shirt?
If you are an entrepreneur or in venture capital you might appreciate (or resemble) some of the sentiments from VCWear.
If you are in a larger corporation, then I know you will find many of these DespairWear demotivators hit a little close to home. I personally like some of the kid products, which are cute and not so depressing.