Rodney Dangerfield was one of the hardest working comedians I've ever seen. Even after decades of huge success, he would still put a huge amount of effort into each Tonight Show appearance, carefull gathering together dozens of new jokes, rehearsing them in small comedy clubs every night for weeks until he was sure he had them in exactly the right order. He'd also tape each tryout and listen to it over and over till he had perfected the delivery and timing of each line. Viewers may have thought he was doing a bit of his regular nightclub act, not knowing he had carefully crafted the routine just for that one Tonight Show.
Here's a typical Tonight Show appearance:
