About different users and their alts on the site, why not just mute them? Or stop replying to them at all? If you really have a problem with them, just don't post in their threads.
Sometimes the simplest solution is the best one.
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Because they simply can't ignore them. Muting makes this easier, but for some, having the "show all hidden posts" or "show hidden thread" is too tempting. Then seeing what that person posts, they can't help but to reply.