Rihanna -- Check Out Tat Bikini

Rockin' her red 'do and skimpy bikini, Rihanna showed off her curves -- and some new ink  on her arm and thigh -- while in Hawaii this weekend.

RiRi is shooting the movie "Battleship" in Hawaii, so the new tats may be for her role and not permanent.

Either way, we like the way you lie ... in the sun.