system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 why is the lowest button hole on a dress shirt horizontal, while all the others are vertical?
gpt
Out bodies tend to twist when we walk, even moreso down near the waist, where that bottom button is.  A horizontal button hole is able to handle more stress from that twisting motion, and since it's (usually) hidden inside pants anyway, it is made horizontal, so that the button is less likely to break off.

The rest of the button slits are vertical, because they simple end up looking better.  Despite all of that twisting motion of our bodies, the buttons always end up generally centered over the slits, rather than always sliding to one side or the other and looking "off."  Also, it's generally easier to fasten buttons in vertical holes.