On some shirts, any or all of the following may be true of the lowermost button/buttonhole:
The buttonhole is oriented horizontally (whereas all the others are oriented vertically)
The buttonhole is lined with a different colour of thread from the others
The button is sewn on with a different colour of thread from the others
I’m not talking about spare buttons sewn onto the bottom corner of the shirt - this is a proper button/buttonhole, it’s just different from all the others - why?
I always assumed that this one was to make it less likely that this button would come undone, thus causing the buttons above it to become undone. Vertical buttonholes are easier to button, but also easily come undone. Having the lowermost one horizontal serves as an “anchor.”
Ah, the next shirt you buy may have it sideways. I notice it mostly on dress shirts. I find it a pain. As Ron said, we did fine for a long time without it. I am quit willing to continue to.
Because the shirt’s opening is vertical. When you pull apart the two sides, the buttons can more easily slide through vertical buttonholes. With a horizontal button, if you pull the sides apart the button slides to the end of the slot and doesn’t come out.
The bottom button has more horizontal stress to deal with than the other buttons, due to the fact that the tails are pulled in different directions . . . especially if the person has a belly. The colored thread may be stronger, and may be used for quality-control purposes (indicating that a stronger thread has been used).
The lowermost button hole, described by the OP, is a better design, but less appealing visually. Since it is intended to be tucked into the shirt, and has to be more resilient, it’s positioned horizontally to help prevent the button from coming undone.
I wonder if this bottom buttonhole style is one of those things almost universal in some countries and unheard of in others.
I’ve been wearing men’s dress shirts in the US for almost 40 years now. Both cheap and expensive. I have never seen nor heard of a bottom button different from the others.
It *is *common bordering on universal for the top buttonhole (the one behind your tie knot) to be oriented horizontally. But I’ve never seen that same design at the botom.
I just checked my closet. Several of my casual “St. John’s Bay” shirts (from J.C. Penny’s - I know I’m giving up my sartorial secrets here) purchased in the last few years have horizontal lower buttons, while others from the same line do not.