Doesn't matter what Wiz Khalifa's name is ... he can't go around peeing in public ... according to Pittsburgh cops, who busted him early Saturday morning for allegedly doing just that.

Pittsburgh PD says it caught the rapper emptying his bladder outside a popular bar called The Flats on Carson ... around 2:30 AM Saturday. There's no mug shot coming ... it's just a ticket.

Wiz is from the Pittsburgh area, and ... of course, one of his biggest hits is "Black and Yellow."

Indeed.