Episode: "Flight 1" (Season 2, Episode 2)
Context: An American Airlines flight goes down, killing Pete Campbell's father, and all the higher-ups at Sterling Cooper see is an opportunity. Except Don. During the argument about trying to nab American in the wake of the accident, Don brings up the fact that the firm already has an airline, to which Roger replies, "We don't have American." Don's response wins points for accuracy and snark.