The term staircase humor refers to the great lines we wish we'd said but thought of too late... Talk show host Phil Donahue once missed a great opportunity when a very attractive young woman stood up to ask a question. She was carrying a baby girl whose face was covered with a checkered bandana. Impulsively, Donahue pulled back the handkerchief and exposed on camera not only the child's beautiful face but the beautiful breast she was nursing on. The audience exploded with laughter and Donahue was speechless. To this day he is hanuted by such staircase lines as, "Anything in there for me?" and "This young lady keeps abreast of the times!"
Sources
Melvin Helitzer, Comedy Writing Secrets, p. 227