Sylvester Stallone Yo, Jennifer ... I'm the King of the World!!!

Good to know even Sylvester Stallone does the Leo in "Titanic" thing when he's on a boat, but most of us can't compete with the view he has right now -- namely, his beautiful wife, Jennifer Flavin!

Sly and the family Stallone are vacationing in Saint-Tropez to celebrate his recent 72nd birthday. While he was playing Jack on Tuesday ... Jennifer and their daughters, Sophia and Sistine, were on paddle boards, attempting what looks like some yoga positions.

The fam's already enjoyed some top-deck time -- sunbathing in their bathing suits -- and now they're looking to enjoy the Mediterranean waters.

If anyone's got it better than Sly ... nevermind. Nobody does.

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