Sam Smith Wears Red Speedo at Miami Beach, Gets Cozy with Mystery Man

RED, HOT SPEEDO!

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Sam Smith hit the beach to cap off the week -- and they bared it all out there ... rocking a de facto Speedo, and showing off some major PDA with a mystery man in the water.

The singer was in Miami Friday, where they stripped down a teeny-tiny bathing suit and got into the water ... with all their tattoos on display, including a Betty Boop one by their leg. There's lots of ink on Sam's body ... and they certainly gave folks an eyeful to take in.

While Sam was splashing around, a dude joined them and got a little touch-feely as well. While they were both neck-deep underwater, this fella started riding on SS like a horse.

It's basically a piggy-back ride in the ocean, and they both seemed to have a blast out there.

Eventually, Sam and their pal were joined by even more friends -- with the whole group greeting one another ... and handing out hugs and kisses. Looks like a big ol' meetup.

It's great to see Sam out and about in the sunshine, and comfortable in their own skin. We know Sam's been on a major body-positivity journey in recent years -- this after struggling with self-image insecurities. Now, they're embracing what they're working with for all to see.

SPEEDO CELEBS -- GUESS WHO!

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Sam tends to be a bit of a lightning rod at times ... but here, they're dishing the electricity!