Brooks Nader's newest photoshoot is probably more appropriate for Playboy than Sports Illustrated's Swimsuit issue ... 'cause she ditched the bikini for an au naturale look on vacay.
The model ran off to Los Cabos, Mexico for a little Valentine's vacation ... and, she decided to really let loose -- throwing off her top and letting it all hang out.
Check out the pics ... Brooks starts with a bright orange top on while her topless gal pal photographs her -- but, she quickly decides to get as naked as her proverbial dancing partner and frees the nipple for the whole beach to see.