Rihanna -- Peek-a-Boob ... Piercing

Everyone and their mother can see right through Rihanna ... literally.

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With her nips -- and nipple piercing -- exposed through a transparent tank top and a pair of Daisy Dukes, the sexy 21-year-old pop star arrived to a restaurant in NYC on Wednesday.

Just like the name of her hit album, she's a good girl gone bad.