We begin with “Popular Teens” from the early 50s, one of the more incompetent comics ever fed to a printing press. This panel tells it all:

In the background, the Blue Man Group is practicing their “Salute to the Air Force” routine; to the left, a red-haired Ed Grimley dork is picking his nose while his mind goes click-click-click saving up this image for later; in the foreground, an instructor  - who has a form of chronic lycanthropy that starts at the wrists and ankles and works its way in – is attempting to show “Miss Gay” how to stand straight up by inflicting irreversible spinal damage. God, how he hates women. And what’s that in the lower right-hand corner? The shadow cast by a skylight, perhaps, but it’s not as though the drawing would have been strangely  incomplete without it.

You can tell it's a gym because it has bowling pins and a beach ball, as well as nipple-level gymnastic rings hung close to the wall. The last guy who tried a fancy routine went right through the window. That's why they installed the wire glass.

Be straight, Gay! Gay! Way up straight! Ha ha, they couldn’t predict the shifts in the vernacular.

Really? Explain the next page, then.