Unless you don't actually watch TV, you have more than likely seen the Old Navy commercials where they reunite old music, sitcom and movie stars for ads about Old Navy Performance Fleece. Or Cargo Pants. You get it. In the past they have brought back MC Hammer, New Kids on the Block, The cast of "Melrose Place" and "Beverly Hills 90210". Now, it's "National Lampoons' Christmas Vacation"