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Nina Dobrev 's got a sunny disposition ... which perfectly matched her surroundings when she hit the beach in a tiny bikini.

The actress celebrated Thanksgiving with some pals in Malibu ... stepping out in a black and white two-piece which provided only bare minimum coverage. Backgrid

Nina carried a coffee with her ... and, she slung a huge beach umbrella over her shoulder -- grinning wildly and surely getting some chuckles out of her companions.

ND went for a dip, too ... making sure her bottoms were secure before splashing about in the waves. Gallery Launch Gallery

It's a low-key holiday for Nina, who has experienced a ton of changes in her personal life over the last few months ... including splitting from her longtime fiancé , snowboarder Shaun White .

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