Everyone has a dark side. The Whitney Museum’s new Sinister Pop exhibit takes a look at the less cheerful side of artists like Andy Warhol, Jasper Johns and Ed Ruscha. Goodbye, bright flowers and oversized soup cans. Hello, limp cigarette butts and faceless mother and child. It’s a fascinating take on a much-studied and oft-quoted era, with nods to everything from film noir and over-consumption to race relations, women’s rights and post-Vietnam War political rage.