Keegan-Michael Key's Tip for Ruth Bader Ginsburg, 'Take Your Vitamins!'

With Supreme Court Justice Anthony Kennedy stepping down, the most important issue in America right now is -- what's Ruth Bader Ginsburg eating today?? This according to Keegan-Michael Key.

We asked Key, of "Key & Peele" fame, just how big a deal Justice Kennedy's retirement announcement really is, and his resounding answer ... IT'S A BIG FREAKIN' DEAL. Keegan and his wife were strolling Rodeo Drive when he broke it down for us.

First off ... he's concerned about how the Court's 5-4 decisions play out in the future -- which is why he's also extremely concerned about RBG ... and her diet.

Fact is, at 85, she's now the oldest Justice ... and, with her decisions leaning liberal -- if she leaves while Trump's in office, the Court could be far more conservative for decades to come.