TIFU by seeing a friend's bare feet, asking their skin care regimen, and discovering that I've had athlete's foot for more than 30 years.

During puberty, the body goes through many changes as a boy becomes a man.
The voice deepens, musculature increases, genitals grow and gain hair, a beard and moustache come in, and the feet develop a hard, protective crust.
All natural physical development.

Or so I had assumed until this weekend, when our "pod" got together at the beach for a little summer fun.

I've always enjoyed walking barefoot on the beach, as the gritty sand tends to wear down the thicker callouses and slough off shedding skin layers.
Sometimes I would even use a pumice stone to sand them down thinner so that they wouldn't tear up socks as badly as when left natural.

Now, I've never really paid attention to feet, never really looked at them closely or had a fetish for them like you hear about, so even with partners playing with their feet just wasn't something I ever did. I've seen women's feet in movies like the toes scene in The Big Lebowski, but assumed women just have softer feet than men. I probably had plenty of opportunities to see other mens' feet at the pool or gym showers, or wherever, but without having really any interest in feet, I can't say I've looked closely at anyone's feet, ever.

But on this day, one of my guy friends was wearing bright purple nail polish.

It caught my eye, naturally, and it occurred to me that somehow his toenails were long and flat, like fingernails, not white and bunched up like toenails. And his protective callouses were almost missing! Not the sanded-down smooth appearance from walking in sand or using a pumice stone, but virtually absent altogether! I wondered if this meant he didn't often walk barefoot, and so never developed them, or if he had some method better to sand them down.

So I asked, "Hey, I noticed your nail polish, your new style?"
"Ha, no, my daughter wanted to practice, and couldn't say no!"
"I couldn't help notice how flat your toenails are, and you have almost no callouses -- do you use some sort of special cream or trimmer to get them to look like that?"
"No, they're just normal feet."
"But you don't have any callouses on the bottom. Normal feet have callouses to protect them when walking on hard or rough surfaces."

And showed my foot as an example.

"Um, wow," he said, "how long have you had that? Are you taking any medicine?"
"Taking medicine? For what? These are just normal feet with normal callouses."
"No, no they're not, that's like the worst case of athlete's foot I've ever seen. How long have you had it?"
"I don't know what you mean ... my feet have always been like this ... this is just how feet are. ... isn't it?"
"No, not at all. That's foot disease. It's some sort of fungal infection. There's medicine for it. Have you never heard of athlete's foot?"

Yes, I had heard of athlete's foot. From TV commercials advertising creams to treat it. But they never showed pictures of it, nobody had ever told me what it was, and nobody for over thirty years after I went through puberty mentioned that there was anything at all wrong with my feet.

Never has a doctor mentioned it to me.
Never has a partner mentioned it to me.
Never has a coach mentioned it to me.
Never has anyone mentioned it to me.

I just thought that's how feet are.

Epilogue: with the obligatory "this happened two weeks ago," I immediately visited a dermatologist the next business day, got a diagnosis and medication, and my feet are already halfway through a magical transformation. It's incredible.

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TL;DR: While going through puberty my feet developed thick callouses and I thought this was a normal part of growing up. Nobody ever told me my feet looked strange, I never compared my feet to others, and I never realized anything was wrong with my feet until asking a friend how they made theirs so smooth and they told me I had athlete's foot for thirty years.
　　　　
^{Edit: typos, formatting, &c.}