Nick Nolte: Down and Out in Malibu!

Nick Nolte was pushing a shopping cart Saturday in Malibu and looked like he hadn't shaved in months ... but fear not -- it's not as bad as you think.

Nick's not homeless by any stretch ... he was shopping at a fancy grocery store.

The 75-year-old may be in a contest with David Letterman, and from the looks of it ... they're covered neck and neck.