Hey Ask Debonair,
While wearing a suit, when is it appropriate to button my suit jacket and when should I leave it open?
Typically, the rule-of-thumb is to fasten the suit jacket while upright that is, standing or walking ˆ and to leave it unfastened while seated in order to avoid any awkward-looking bunches.
For a single buttoned suit, it should go without saying fasten the only button available. As for a two buttoned suit, fasten only the top button. With a three button suit, the fastening of only the middle button is advisable, yet if you must (and really, only if you must) the top button may be fastened but only with the middle button as well. Please, never fasten the bottom button (again, unless it is the only button), certain things are best seen and never used.
This is hard to belief that most men don’t even know how to do this correctly. This is a great post that will help you out