Once I was researching something and found wrong answer on SO from some junior dev from India. The answer was wrong and it was evident that the author of the answer didn't even fully read the question. Out of curiosity I checked the author's profile and found out that it was a deliberate strategy: e.g. when there's a question about working with files, he'd post an answer with a link to the language page on "open".
I politely asked the author in the comments to stop posting wrong or useless answers. Instead, he wrote very aggressive response, opened my profile and downvoted as many of my answers as he could.
And there were many similar cases, probably still are.