Irina Shayk's Teeny Bikini Goes Missing, Bradley Cooper Misses Out

We're not really sure why Irina Shayk even bothered with this bikini.

The supermodel was on vacay with Bradley Cooper -- they moved on to the Italian isle of Sardinia.

Looks like Irina was solo on the beach as her butt was devouring a micro bikini. Bradley? For some reason he was playing tennis.

Julia Roberts said it best ... big mistake, Bradley. Huge.