Jimmy Kimmel's intrepid gotcha! team asked a host of gluten-free pretty people about what constituted gluten. The best answer is when an inexplicably shirtless gentleman says: "Gluten is in bread; it's a flour derivative, wheat [COUGH TO THE SIDE]." The old instant-fake-a-cold trick! Wonderful.
In fairness to these souls, sometimes you don't quite know the thing you are afraid of. Fear is fear itself. For some people, gluten is their fear of the unknown, which is also a thing that certainly is in bread and makes you chubs.