John Calvin was a theologian and pastor during the Protestant Reformation and many of his ideas are still widely regarded in Christianity today.
But he's not such a stuffy guy. In fact, Calvin liked flowers. He figured everyone liked flowers as much as he did so he used the acronym TULIP to explain the most important things about God:
Total Depravity Unconditional Election Limited Atonement Irresistible Grace Perseverance of the Saints
(Hey, I know some of those words!)
So, read up on Calvin, TULIP, and stop to smell the flowers every once in a while — you might run into someone who wants to know what your shirt means. It's an easy way to break the ice and start talking about Jesus.