I see some chefs with the top button unbuttoned, and many who button it.
I've seen, in a couple of culinary school student manuals, instructions on
how to wear the button: one student manual said all students had to button
it, the other one said it could be unbuttoned.

What's up with the top button of a chef's coat? Buttoned, unbuttoned, is
there special etiquette? Anybody know?