I am honestly kind of surprised anyone cares what you wear in the back if it’s neat and not eccentric. We are carrying basic economies wearing tattered wifebeaters soaked through with a mixture of sweat and McDonald’s honey BBQ. I see no reason to deny a cabin seat in coach to a guy in jeans and a button-down.

The cockpit is a different story for all the reasons mentioned previously. The pax are expecting to see a certain (very high) level of professionalism coming from the people in there.