Seinfeld famously began and ended with a thoughtful discussion on the importance of a dress shirt's second button (it "literally makes or breaks the shirt.") While I do totally agree with him, I also believe that the bottom button--specifically the bottom button hole--is an unsung hero of clever design.
Have you ever noticed that sometimes the bottom button hole is vertical like all the rest of them, but every so often it's horizonal? I always wondered why until the the other day. I was admittedly struggling a little bit to unfasten the penultimate button, having a hard time getting the angle just right. Eventually I got it, and I happened to notice that after that struggle, the bottom button came open like a dream. "That's odd," I thought, until it hit me: the bottom button hole is horizontal so that it's easier to open and close. This angle makes total sense since you're coming at it from the top vs. from the side, as with the upper buttons.
What a wonderful example of someone putting thought into something that makes our lives ever-so-slightly easier, even though we may never notice.
Now the only question is why they don't put the penultimate one at a diagonal...