So what is shortsheeting a bed anyway? And why is it hilarious?

That sentence you quoted went with the one before it:

and the “you” referred to those children who were taught, when I was a child in the 1950’s, to tuck the sides in (and who were probably also the people doing the shortsheeting and having it done to them.) It wasn’t meant to refer either to you in particular or to the entire population of the planet. Sorry if that was confusing.

I’m tall, and for ~10 years I slept curled up. If I was tired, and got into a short sheeted bed again, like I had at age 9, I’d probably just curl up and go to sleep.

But normally when I get into a bed tucked at the bottom, I kick it free. Nowhere to put my size-13 feet in a bed tucked at the bottom, I just don’t fit.

I gotta say, i was taught that, but as an adult, i don’t see the point, and mostly leave my bed untucked.