ANOTHER Naomi Campbell assistant has bitten the dust. The sybaritic supermodel parted ways with her latest underling on a British Airways London-L.A. flight last week. Before boarding, Naomi was heard complaining on the phone about service. Then, she turned on her assistant. "Naomi was angry because some dresses didn't get where they were supposed to go, and the assistant yelled that she was quitting," says our snitch. "Passengers complained to the stewardess, who was going to get the pilot, when they stopped their screaming match. Then they didn't speak to each other for several hours." Campbell's rep didn't return calls.