Donald Sterling -- Ultimate Cash Cab ... Billionaire Hails Taxi

Here's something you don't see every day ... a multi-billionaire hailing a cab.

Donald Sterling -- who recently sold the L.A. Clippers for $2 BILLION -- was out in Bev Hills Wednesday when he decided to catch a cab to go home.

Interesting, considering most billionaires in this city either drive themselves ... or use a private chauffeur ... or at least use Uber LUX if they're gonna hit the town.

But not Sterling ... who quietly got in the back seat and was quickly whisked away.