The rules for the buttoning of jackets and waistcoats seem to always route back to Queen Victoria's son "Bertie" Edward - The Prince of Wales, who would eventually become King Edward VII. He was rather a stylish fellow and loved a good time, unlike his mother Victoria. She was dour at times with a gloomy outlook and style as she continued to morn the loss of her husband Albert.
After a little research, here's what I have discovered about the buttoning rules and their origins.
A way to remember the general rule with a 3 button jacket or waistcoat is to repeat "Sometimes, Always, Never".
Which means that you can button the top sometimes, always have the middle button fastened and never do up the last button.
If you have a 2 button jacket/waistcoat then always fasten the top and never the 2nd button.
But why is this the case?
In the first few years of the 1900s the single-breasted suit came into being. It was designed for a more comfortable, casual look. With a relaxed fit, it looked good also when the wearer was riding a horse.
Therefore, the suit also known as the "lounge suit" became very popular for horse riding. The original riding jackets bottom button was positioned below the waist, so a rider had to have the bottom button undone when in the saddle.
It seems that Edward VII thought the top button of a jacket looked much better undone. He also kept the bottom button undone as a matter of habit or indeed as a 'nod' to the original riding jackets the lounge suit replaced.
Hence the rule seemed to come into being, as Bertie was somewhat of a trendsetter at the time!
The bottom button of the waistcoat being undone has more of a basic reason. As I mentioned earlier Edward liked a good time. It's reported that he had several full meals of high-calorie foods every day, and smoked like a chimney too. As you imagine he amassed quite a bit of weight with all the years of overindulgence.
Therefore, for comfort, he stopped buttoning the last button of his fitted waistcoats. He expected those around him, within his court, to dress as he did leading to an unwritten "law". A law most of us chaps adhere to, even now!
In our opinion, you should wear clothing in a way you think looks best for your shape and your taste. Afterall, these rules have all been instigated by others at some point in history anyway. So why not create your own rules?