The sort of button-down shirt worn by a man who has an overly inflated midsection. The Gutton-Down slims and hides the protruding belly fat that can be unsightly when a man wears a t-shirt.
Note: Vertical stripes are favoured.
Man, Leon has put on a bit of weight since he broke up with his girlfriend. It's a good thing he's sporting his new Gutton-Down, it helps to make him look slimmer.