Today I saw a behaviour which really surprised me:
I answered the question and then after a minute another guy answered it as well. The answer was basically a duplicate of my answer (which was not a surprise, the question was simple). I checked him, because he was quite reputable guy with 21k reputation.
Then I saw that my answer was downvoted. So the answer of another guy (not the guy with 21k, who also happened to have similar answer to mine). I was surprised, because both our answers were correct. But then I decided to check one more time the 21k guy who was not downvoted.
To my surprise I saw that right now he had +2 downvotes in his statistics. This was extremely lame. He basically downvoted two correct answers to be on top of the results.
Is this behaviour acceptable and what should a person do if he sees or suspect such behaviour? I was lucky because I saw two opened page and was able to see the difference in votes and it happened in less then a minute so I was pretty sure that he downvoted correct answers.