Without speaking about how much the issue occurs, there’s what I think is a fact: Watched Words won’t work against such behavior. If someone wants to post an offensive word, they’ll find a way to do it.
As an admin of a few Discourse forums, I’d handle those manually.
Maybe have a look at Discourse Fingerprint - Browser Fingerprinting Plugin if you think problematic users could be aggressive enough to create multiple accounts to achieve such a purpose.
But now I’m talking more as if it was a support or a community topic… 