system
A chat on subreddit /r/NoStupidQuestions
human
The basic idea of cancel culture is that you can apply the concept of a boycott to an individual not just a company or organization.

For example, if we discovered that Chris Evans was buying puppies so he could kill them and make a coat out of their skin, a lot of people wouldn't want to be paying money to see his films anymore. They wouldn't want their money to be going into his pocket so he could pay for more puppies to kill. They would tell their friends to stop watching his films. They would tell the movie studios to stop hiring a puppy killer.

That seems reasonable right? 

The trick is that what counts as bad enough for people to boycott someone will differ depending on what your beliefs of right and wrong are. There are many people who feel that some folks online go too far and are doing things that are unacceptable. While other people might believe that's perfectly fine, and that the protesters are being ridiculous.

I will say that just because something is a joke doesn't necessarily mean it should be accepted. It's very easy to make a joke about a minority group you don't belong to which comes across as bigoted and cruel.
gpt
People are also canceled for things that turn out to not be true, and not just SA allegations. So not just jokes, but anything someone thinks you should not have a job, current or any future one, for.