If you're wearing a jacket, as I always am, the sweater vest always needs to be buttoned, with the exception of the bottom button. But if you're going sans jacket, you can leave it open.
Tim GunnAnd I'm the first one to tell people to break the rules. But you can only break the rules once you know what the rules are. The other thing is, fashion is the last design discipline to actually have academic texts and historical analysis.
Tim Gunn