I found the funniest t-shirt site. It is called Despair Wear. For the cynic and pessimist, it is a gold mine.
The caption reads: Not everyone gets to be an astronaut when they grow up.
I also love Threadless. The visual pun and the word play makes for something orginal and authentic. In a world of mass production, I prefer to have something unique. T-shirts are the epitome of planned obselescence but I think the ultimate irony is to make them a tiny piece of pop art.  This is an example of a threadless T-shirt.
Titled Running Rhino