Jared Leto Life o' the Party ... A St. Barts Yacht Bikini Party!!!

Jared Leto's surrounded by a throng of bikini-clad women on a Caribbean island ... and it's pretty clear he's the straw stirring the drink.

The "30 Seconds to Mars" frontman was cruising on a yacht Wednesday in St. Barts with a bunch of very eye-catching friends ... including several women in bikinis and some ripped dudes. It's in the 80s down there -- like always -- so they're feasting on some Vitamin D.

Jared and co. came ashore to stroll the perfect white sand beach and snorkel in the crystal clear waters.

Vacay's looking up for JL cause this sure beats the hell outta watching someone getting pummeled.

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