The hamburger zealot was so fanatical about his burgers that he camped outside his favorite fast-food joint for hours every morning, waiting for it to open. And he would never put mustard on them, only ketchup.
The original zealots were a group of first-century Jews who were absolutely determined to overthrow Roman rule in Palestine. Today, anyone who goes overboard in their zeal, or enthusiasm, for a particular cause, a religion, a sports team, or a charitable organization — can be called a zealot. The coffee lover was a zealot regarding where his coffee was grown, who grew it, and how it was roasted.