Slash and burn. If you have a black long-sleeved dress that shows some cleavage, you can be Bellatrix Lestrange (left). Tear along the arm seams and (carefully!) singe the hem and cuffs with a match (keep a wet rag handy to snuff the flame as soon as it catches). Add a wide black belt, knee-high black boots, bold lipstick, dramatic brows, and a long black wig. Done!
Think British. "Costumes should be a laugh," Temime says. "The English have a beautiful ability to make fun of themselves. If you arrive at a Halloween party and everyone laughs at your costume, congratulations—you've broken the ice."
Next: Get a brief history of Halloween