I didn’t watch The Tonight Show when Ed McMahon was on; I mostly knew him from Super Bloopers and Practical Jokes (meaning I thought of him as Dick Clark’s sidekick rather than Johnny Carson’s) and those American Family commercials that everybody seems to confuse with Publisher’s Clearing House.
Johnny’s jokes about McMahon’s drinking — a staple of the show — were like a throwback to an older era of show business (since they were holdovers from that era), where over-indulgence in social drinking was considered funny. As Carson pointed out, it was a throwback to Jack Benny making jokes about Phil Harris’s drinking. A host would not normally do that today, because alcoholism isn’t considered a laughing matter, and because entertainers no longer want to be thought of as people who drink too much; but back then, you’d have entertainers who actually pretended to drink more than they did — Dean Martin, most obviously — because being thought of as a drunk was good for your image and good for comedy.
I couldn’t find any clips of Ed’s role in Butterfly with Pia Zadora, but here’s a trailer for one of the two most insanely stupid films of the ’80s (the other being Pia Zadora’s The Lonely Lady). Joe Queenan commented that McMahon was cast as Pia’s father-in-law, as well as one of the few people in the movie she doesn’t sleep with, because he was the only person in the world who would be “credible as a man who would welcome Pia Zadora into his family.”