Re: repeat after me
In one episode of https://en.wikipedia.org/wiki/Studio_60_on_the_Sunset_Strip
- Aaron Sorkin's series set inside basically "Saturday Night Live" - a writer under pressure used a stolen joke and got hell for it. It turned out to have been stolen and stolen and stolen, ultimately from the "Studio 60" show. This is fiction.
Bob Monkhouse was perhaps unfairly called "The Thief of Bad Gags" - because that was Milton Berle - Bob collected them but may have not used them. And I've got an autobiographical book by Jasper Carrott where he remembers as a folk club MC going to watch circuit comedians and steal their lines. Including an especially fruitful occasion watching Bob Monkhouse.
But admitting it in print doesn't make it right.
Anything uttered in public can still be copyright, I think - but that doesn't mean that you will be able to stop infringement.