It was, as Kris Jenner would say, “a case for the FBI.” When Diane Keaton posted an Instagram of herself in high-waisted, wide-legged pants, the Internet went into a frenzy. The caption read, in all-caps: “I’VE NEVER RECEIVED MORE COMPLIMENTS ON ANYTHING I’VE EVER WORN IN MY ENTIRE LIFE.” While Keaton shared everything about where…