Hard cancellation is when you get others to gang up on them and go to HR to try to get them fired. Afterwards, you publicise whatever got them fired offline in the hopes that they become 'radioactive' to employers and so that they and their family fall on hard times.
I'm a little confused as to why people don't understand what "cancel" means in this context. Isn't it quite a popular topic nowadays? Is it possible that they're claiming ignorance, because they want to argue against the meaningfulness of the term?