Heidi Klum Suns Her Buns, Boyfriend Takes a Bite

Heidi Klum's BF is a serious brown-noser -- and a lucky son of a bitch.

Klum and Vito Schnabel got very playful Thursday in St. Barts, where he was happily -- we're sure -- behind her efforts to get up on a surfboard.

Check out the pics ... Vito caught a few waves, but Heidi was satisfied sunning her buns on the board ... which seemed just peachy to him.