High praise...?

What direction did you give Leslie for that ['don't call me Shirley'] scene?
Jerry Zucker: I think we had shown him Zero Hour! previously because we wanted him to see the style. We told everyone that “playing it straight” doesn’t quite do it, because they think they have it, but they’re still winking. We told them to play it like they don’t know they’re in a comedy. Like no one told them. Just the way Leslie would have played this in The Poseidon Adventure, or any other of the films or television shows he had done. Leslie, more than anyone, really got that and relished it. He loved it. For the whole movie, Leslie didn’t need a ton of direction on performance.

David Zucker: He just jumped into the water and swam. He knew what he was doing.

Abrahams: You can intercut scenes from The Poseidon Adventure with his performance in Airplane! and you can’t distinguish, performance-wise, between them.

(link)