PETER GABRIEL played a show in Hollywood on Saturday . . . and just as he was launching into "In Your Eyes", JOHN CUSACK ran onstage with a BOOMBOX.  Of course, it was a reference to the 1989 movie "Say Anything", where John's character stands outside the window of his ex-girlfriend's place . . . holding a boombox playing "In Your Eyes" over his head.

(John comes out 20 seconds in . . . here's the clip from "Say Anything".)