Doonesbury by Garry Trudeau for January 29, 1971
Transcript:
Girl: Hey, B.D. Isn't that Mike swimming down there swimming underwater? B.D.: Yeah, I guess it is. Girl: Wow! He's been down there for ages! What stamina! B.D.: I'll say! Girl: From the looks of things, he's practicing underwater maneuvers! B.D.: Oh, no, I disagree. He's just building up his lungs. Mike: (Actually, what I'm really doing is drowning.)