The Underwear Under Swim Shorts Thing Every Man I Know Does Without Explaining Why

My brother-in-law packed for our lake trip last summer with the kind of precision I usually reserve for carry-on liquids. Swim trunks, rashguard, the good sunglasses. And then, folded into a neat little square on top, a pair of boxer briefs. To wear under the trunks. Which already have a liner. Built in.

I said something about it, not even mean, just genuinely confused, and he looked at me like I’d asked why he bothers wearing pants at all.

That’s the moment I started actually paying attention, because once you notice it, you cannot stop noticing it. My husband does it. My dad does it, and has for as long as I’ve been alive. The guy who mows our lawn showed up in swim trunks over what was unmistakably a pair of briefs when he jumped in our neighbor’s pool during a heat wave two summers ago, fully clothed underneath his swimwear, like he was expecting an OSHA inspection. This is not one weird guy with a preference. This is apparently a load bearing pillar of American manhood that nobody agreed to explain out loud.

Nobody Told Them To, They Just Do It, Like It’s a Rule Handed Down at Birth

Here’s what gets me. Ask any one of them why, and you get a shrug, or a half sentence that trails off, or “it’s just more comfortable,” delivered with zero follow up detail, like comfort is self evident and I’m the weird one for asking. My husband’s answer, word for word, was “I don’t know, I’ve always done it.” Twenty nine years old. Cannot tell me why he’s wearing two layers of underwear to go swimming, but he’s done it his whole life, so apparently that settles it.

I’ve come to think it’s not really about the swim trunks at all. It’s about the liner. That mesh netting sewn into most trunks is genuinely one of the worst pieces of fabric engineering I’ve encountered, and I say that as someone who has bought and returned a truly embarrassing number of swimsuits. It rides up. It chafes in exactly the spot you’d expect. It gets that specific kind of wet where it stops feeling like fabric and starts feeling like a used dish sponge, and it stays that way for the rest of the day because it’s not actually designed to dry fast, it’s designed to exist quietly and be forgotten about, except it never is. So the boxer briefs aren’t really an addition. They’re a correction. A guy puts on the underwear his body already trusts because the thing the swim trunks came with has never once earned that trust.

And once one guy in a friend group does it, that’s it, that’s the whole culture now. Nobody’s out here having a debate about liner efficacy at the pool. It’s word of mouth, or more accurately, it’s watched, silently, by every younger brother and locker room neighbor who ever noticed the shape of someone’s shorts and filed it away without asking a single question. My dad learned it from somewhere, never told me where, and my husband will hand this down to our son with the exact same lack of explanation, and it will just keep going, an entire lineage of men doing a slightly redundant thing because asking why felt more embarrassing than just doing it.

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The Part Where I Admit It’s Actually Not That Dumb, Which Physically Pains Me to Type

Okay. I spent a while ready to write this whole piece as one long joke at their expense, and then I actually tried it. Borrowed a pair of my husband’s compression boxers, wore them under a pair of swim shorts on a trip to Lake Michigan, mostly to prove a point to myself. And I hate reporting this, but the point did not go the way I wanted. There was no chafing. There was no shifting around every time I got out of the water. The whole lower half of my body felt held, in a way that a mesh liner has never once managed to make me feel, not in fifteen years of swimsuits, not for three hundred dollars, not for thirty.

So fine. There’s a real mechanical reason underneath the shrugging. The liner in swim trunks is built for modesty in the water, not support out of it, and the second you’re doing anything more athletic than floating, that gap becomes obvious fast. Add underwear underneath and you’ve basically built yourself a rashguard for the one area nobody wants irritated on vacation. It’s not really about being modest twice, it’s about one layer that’s decorative and one that’s doing the actual work.

Where I still think they’re being ridiculous is the total absence of any acknowledgment that this is a workaround for a design flaw rather than a personal preference, stated as if it’s just how bodies work.

Say the shorts have a bad liner. Say the liner chafes. That’s a complete sentence, it takes four seconds, and instead I get a shrug and “I’ve always done it,” which tells me nothing except that this entire habit runs on inherited silence instead of actual information passed between men who apparently love each other but won’t compare notes on underwear.

I still give my husband a look every single time he layers up for the pool, mostly out of habit at this point, the same reflex I’d use on anyone folding a second pair of shorts into a beach bag without a word of explanation. He still doesn’t explain it. But I’ve stopped needing him to, because I found out myself, the hard way, in a lake, that the mesh was never going to hold up its end of the deal. The underwear isn’t the weird part anymore. The swim trunks are.