Jason Alexander was bummed out on a recent episode of his Really No Really podcast. He’d recently discovered that Armin Shimerman, an actor who had guest-starred on the Seinfeld episode “The Caddy,” had a terrible experience with the cast. “I hated them. Hated them,” Shimerman reportedly said during a Q&a at a fan convention. “They were non-communicative, ugly, non-responsive. What’s the word? Insular.”

Maybe Alexander could have chalked it up as a “somebody having a bad day” complaint if not for hearing a similar comment from another guest who just happened to be a former New York Met and National League Mvp. “Keith Hernandez said I in particular was — I think the word was standoffish,” said Alexander.

Was the Seinfeld cast really that rude to guests? For confirmation, Alexander turned to his podcast guest Wayne Knight, the comic actor who frequently played Newman on the sitcom. “I...