Old Fashioned
Season 1, Episode 1, “Smoke Gets in Your Eyes” (2007) · Don Draper
In the series' opening scene, Don sits in a Manhattan bar working out a Lucky Strike pitch on a cocktail napkin and orders another Old Fashioned.
Sources: The Press Democrat - Best cocktails for 'Mad Men' finale; BAMF Style - Mad Men 'Smoke Gets In Your Eyes'; Wikipedia - Old fashioned (cocktail)