This made me chuckle. Randall Monroe is a NASA roboticist who produces the incredibly funny xdcd online comic strip, which specializes in super-nerdy math humor. He also recently created the t-shirt pictured above: The first panel is on the front, and the second panel is on the back. As he describes it on his web site:

Science: We finally figured out that you could separate fact from superstition by a completely radical method: observation. You can try things, measure them, and see how they work! Bitches.

The graph on the back of the shirt is data from the COBE mission, which looked at the background microwave glow of the universe and found that it fit perfectly with the idea that the universe used to be really hot everywhere. This strongly reinforced the Big Bang theory and was one of the most dramatic examples of an experiment agreeing with a theory in history -- the data points fit perfectly, with error bars too small to draw on the graph. It's one of the most triumphant scientific results in history.

(Thanks to Kevin Cornwall for this one!)