Shawn and Marlon Wayans as Kevin and Marcus Copeland in White Chicks (2004)
Cross-dressing is rarely plausible (See: Jack and Jill, The Nutty Professor, Hairspray) but cross-race-dressing? That shit should never be attempted, ever. The Wayans brothers impersonating two white heiresses is the least believable drag we've ever seen. Rather than looking like two rich white girls, the duo looks like a pair of car accident victims whose faces have been replaced with someone else's (in this case, someone who looks like Tori Spelling), and the result is nothing short of terrifying.
Plus, their rendition of Vanessa Carlton's "A Thousand Miles" still haunts us, and not in a good way.