It’s very difficult to state where the line might be. Often it’s the delivery, or the audience or some other factor than merely the words spoken that convey the intent of the joke.
Some people have very clear lines. To each their own, but saying, “you can never joke about x or y” is too far for me. I’ve seen comedians do sets about their personal experiences with cancer and rape and they were great. Sometimes jokes which are offensive or just uncomfortable to some are coping mechanisms for others.
It’s all about context and intent.
