Ignore the annoying and they will eventually get bored and go away. Move on with a thread like nothing ever happened. Don't respond. Don't react. Don't participate in conversations with a user that bothers you. And don't talk about them in other posts.
People who pollute forums ... Don't respond (to them). Don't react. Don't participate in conversations with a user that bothers you.
I saw this thread, and thought, "yawn... drama queens both of them." ... Don't appoint yourself the sheriff or the judge.
Excuse me if this is in the wrong part of the forum
Captcha is a really great idea. It needs to be something tough, though