He is the whitest of the white trash, the kind of man who dumps raw sewage in a storm drain and kidnaps your boss as a Christmas present. And the only man to ever combine a leather belt with a bathrobe. Randy Quaid has played lovable moocher ‘Cousin Eddie’ in four separate National Lampoon films, but his most famous performance still resides at yuletide. National Lampoon’s Christmas Vacation (1989, directed by Jeremiah C. Chechik) has weathered years of apathy to become something of a seasonal favourite. Watching Chevy Chase’s bipolar family man Clark Griswold lose his rag every December is now a festive tradition . Yet Clark is not really…