JACK?. . . JACK WHO?

BEAT IT, YA BUM!

High-tech security cameras at one of LA's poshest private schools spotted what looked like a homeless guy in raggedy clothes banging on the locked front gate. Staffers refused to buzz him in, then heard him shouting over their high-tech audio speakers -- and finally realized that he was saying: "It's Jack Nicholson . . . I'm here to pick up my KIDS!"