Except for “Cossie” I’ve heard all of them used for bathing suits. I actually think that I use bathing suit more than anything else. My Irish friend calls them togs. Briefs are what most people would call a Speedo, Jammers are the tight suits that come down to about the knees.
I usually wear a Speedo and drag suit when I swim laps, a jammer if I’m doing a meet or open water swim, and board shorts I guess at the beach or at the pool normally.
Wow, bold choice. I’m not sure I see the connection though.
I love that some people say “bathing costume.” But it makes me think of this
https://images.app.goo.gl/unjc7KPGSHs9PXzi9
Is “Cossie” pronounced with an “s” sound, or is it “cozzie”?
Isn’t that a synonym for budgie smugglers?
Which, by the way, are my favorite terms, which I do use even though they’re not my dialect, for what I grew up calling a Speedo (regardless of brand). Hmm. I Googled, and there seems to be a wide variety of things that people use this term for, including Speedos.
I grew up mostly in Florida. When I was a kid, we used "bathing suits, or, in clear contexts, just “suits” as the collective term.
My terms are updated and more specific now. I think the terms I use are all understood where I am on the West Coast. Budgie smugglers and banana hammock may not be well known here, but, most people seem to get it (and chuckle).
Another thing here on the West Coast – not only do people use “board shorts” to mean something specific, but some people even know what a “board-shorts connector” is.
I’ve only heard “cozzie”.
Every time I see this thread, I think about The Stranglers’ Peaches.
Will you just take a look over there
(Where?) There
Is she tryin’ to get outta that clitares?
Ostensibly, ‘clitares’ is a French word for a bathing suit. (When I first heard this, I thought it was a brand of French bathing suits.) Looking it up now though, I see post after post of people – including native French speakers – saying this is not true.
Still, I think ‘clitares’ is a perfectly cromulent word for a woman’s bathing suit.
I keep noticing the first four letters.
My ignorant and therefore faux French pronunciation isn’t helping.
Perhaps they did it on purpose. Hmmm.
Fwiw, i always admire a man with a full pelt. I don’t understand the current fad to shave it away. But i understand it’s a huge nuisance with sun screen.
I probably use “bathing suit” as the generic. There are lots of types of bathing suits. My husband wears swim trunks. I like a Speedo style one piece suit. (Yes, Speedo sells full torso suits for women, as well as tight tights for men.)
It does for me. 
Swimming? That’s an activity that involves getting in water that is over your head and then thrashing around to avoid drowning, right? Nah, I don’t do that, and it’s served me well for 76 years.
I rarely go into the water, but spend lots of time on the beach. I wear a big, baggy swimming trunks that I bought 18 years ago and I’m still wearing it. I checked the tag out of curiosity and the brand is Speedo!
Pretty much the same for me. “Bathing suit” is something women wear. I generally think of a one-piece when I hear “bathing suit.” I say “swim[ming] shorts” or “swim[ming] trunks.” I’m from Chicago.
Gotta admit I’d never heard ‘jammers’.
I think of Speedos as being more the size of bikini briefs than standard briefs (or what used to be standard briefs before men’s underwear started going every which way) which is what I’d call trunks. IME, trunks cover the torso from the waist on down, whether or not it covers some of one’s legs.
I wear the same shorts I use for running. I swim in shorts.