Sometimes, always, never. If you’re a man wearing a three-button blazer, those are the only three words you need to know. The middle button should always be fastened. The top button is up to you. But the bottom button? Don’t even think about it.
But where did this fashion edict originate? In the grand scheme of things, it’s a rather new rule. Over a century ago, there were no hard-and-fast buttoning guidelines. Some jackets had five or more buttons, and you could fasten them in any combination you pleased. That all changed when England’s King Edward VII—then the Prince of Wales—started growing a belly in the late 19th century.
Edward liked to eat. A lot. On a typical day, he’d mow down a plateful of bacon and eggs for breakfast, a tower of roast beef and shortcakes for lunch, and a 12-course dinner. A 48-inch waist—the same bulge Henry VIII flaunted when he first sat on the throne—was a little too big for the future king to handle. Edward grew so quickly that he couldn’t fasten his waistcoat’s bottom button. Deciding that he liked the look, he kept it unbuttoned.
In an age before models and TV stars, royals like Edward influenced most fashion crazes. So when Edward kept that bottom button undone, people noticed. A trend caught on, and men of all sizes have been leaving that bottom button open ever since. Nowadays, blazers are designed to keep that bottom button undone. Buttoning it can cause a well-fitted jacket to tighten too closely, making it uncomfortable and unsightly. So although the rule has arbitrary origins, over the years it has become both practical and fashionable.
Incidentally, this isn’t the only fashion trend Edward started. You can thank him for the tuxedo, too! When Edward was still a prince, he wanted a slightly more casual alternative to the extremely formal dinner attire of the day. He opted for a blue jacket, black trousers, and a bowtie. In 1886, his American friend James Brown Potter brought the style to Tuxedo Park, NY, from which it has spread to wedding parties and proms everywhere.