From Don Draper’s old fashioneds to Roger Sterling’s smuggled-in Stoli, cocktails have played a deliciously major role on AMC’s “Mad Men.” But was it really that great an era to drink? Because though the show celebrates — and has boosted modern-day interest in — classic cocktails, it is set in a decade, the ’60s, when mixed drinks were sliding into a sugary slump, says drinks historian David Wondrich. “Cocktails were struggling because they were kind of for the square, old-establishment types, they weren’t for the new generation,” says Wondrich, drinks columnist for Esquire magazine. But if the drinks weren’t particularly exciting, the “Mad Men” era was the best of times for the cocktail scene setting. “The culture of the cocktail really exploded in the ’60s,” says Maureen Petrosky, author of “The Cocktail Club.” Suddenly there were cocktail dresses, new glassware, bar couture, Tiki drinks. The cocktail hour had its own wardrobe.