To be fair I still do these things but only when I’m alone.
Personally I love finding big puddles and then dig drains with a stick or my heel and watch the water flow.
Also love to throw a piece of wood into water and then toss stones high up in the air and try hit it imagining it’s a warship I’m trying to bomb.
Then also without going into details there are some pieces of clothing I would like to wear but don’t because they’re considered femine or gay.
Eh, no biggie! People do that when they don’t experience a similar behaviour themselves.
As for the not that deep crowd, I always thought they’re either self conscious or fear touching a triggering topic. Refusing to engage means they won’t be judged on their opinions or ability to reason and express themselves. Trying to pass a cool is what gives away they’re trying to cover up something.
I think part of it is them being self conscious but I think it was also just seen as a “cool” way to behave like you said. I often saw this mentality on reddit of course and in various discord servers where people just couldn’t back up what they were saying - so someone else approaching them with an in depth take, just causes them to try and shut things down with “oh its not that deep”.
Like its a very dismissive phrase meant to shut down conversation.