I remember years ago Bob Barker caught some lady fast asleep in the TPIR audience, and couldn't resist pointing it out, and during commercial, they put up a still of her face, with the caption "Having a wonderful time"
Steve Allen also spotted someone fast asleep in the audience once on his late night show. The entire audience had already left. Steve just adlibbed and joked around while sitting right next to the guy until he woke up.