[coldtea]

>Is it really plausible that no one thought to feel manly about cold showers until a bunch of nerds came along?

No, but it's quite plausible that it was a niche thing that might have been a fad at some points in the past, only to be revived by a new generation that includes many fad-chacing types, SV people, and BS-artists (aka influencers)...

[luckylion]

I'm pretty sure cold showers have been a thing to show your ability to live without comforts ever since hot showers became a possibility.

And the term fits here, I believe: cold showers do very much wake you up and bring you into reality quickly. There's no dreaming about hypes when you're under a cold shower.

[MayeulC]

An old fad, probably. Romans did this: https://en.wikipedia.org/wiki/Frigidarium