Funny, maybe I'm a tool for even wading into this discussion, but I've always wondered about this.

I know a men's suit jacket should always have the bottom button unbuttoned. That's the way they are cut, to allow for that.

But we're not wearing a "traditional suit jacket," we're wearing a uniform coat, and something from my former Air Force days says to me that all my buttons on my uniform jacket should be buttoned.

Having said that, I usually wear my airline jacket with the bottom button unbuttoned.