If you tell a joke that you heard from somebody else to a friend you're breaking the Copyright of the creator of the joke.

If Copyright was strictly enforced it would constantly intrude in people's lives and pretty much everybody would turn against it.

You don't need to copyright it. Everything is copyrighted by default. You can decide to relax your copyright protection if you want, but the © symbol isn't some magic spell. The sign kinda makes it look like it works the other way.