A couple favorites:
lol, I've been upstate and got to see people work out in the most insane ways.
They stopped letting inmates have free weights in state prisons in PA so they had to switch to machines.The rumor was that there used to be lift offs(like how they let guys have sanctioned boxing matches in graterford backin the day) between the guards and the inmates but the inmates started surpassing the guards in a big way.
I straight up watched dudes max the weights out on the machines, and then have a grown ass man stand on top of the weights to add more weight to what they were lifting. Also, that youtube video you linked where dude is doing handstand push ups, people really do them, quite a lot actually.
I saw a dude, ugly as sin, walk around with an 8 pack of abs. He would do pull ups and instead of counting the pull ups, he would just time himself, continuously going up and down for minutes at a time. I thought I was going to have to fight him because he was into shaking down white kids for their store (I was 19 when I saw him, 6'4" and about 165 pounds) but I had a reputation by then for fighting regardless of whether or not I would get my ass beat and he started going after this kid I went to elementary school with who I let everyone know was a sex offender..
Craziest thing that's workout related was just the people in general though. 50+ year old guys, balding, teeth all fucked up, but when they took off their shirts they were built like a collegiate athlete.
Sorry for the wall of nonsense text. Just saw those videos and it brought me back to a time in my life in a big way.