user-1: Sometimes when I criticize one's post or comment, the user go mad and vote some of my questions and answers down. It is not usual situation to have three down voted answers within 5min and It isn't a pleasant situation for me.
What should I do in this situation if I know the user?

user6: In general, flag for moderator attention and explain the issue. We do intervene in cases of serious misuse of the voting system and will invalidate votes and suspend users, if necessary.
Users are free to vote on posts based on their own criteria, the major restriction is that targeting posts by a specific user with votes is not allowed. Downvoting a lot of posts from a specific user is prohibited just like creating sock puppets and using them to upvote your own posts.
In this specific case there is no indication that any user is targeting you specifically with downvotes.

-1: <p>Sometimes when I criticize one's post or comment, the user go mad and vote some of my questions and answers down. It is not usual situation to have three down voted answers within 5min and It isn't a pleasant situation for me.</p>

<p>What should I do in this situation if I know the user?</p>
 6: <p>In general, flag for moderator attention and explain the issue. We do intervene in cases of serious misuse of the voting system and will invalidate votes and suspend users, if necessary.</p>

<p>Users are free to vote on posts based on their own criteria, the major restriction is that targeting posts by a specific user with votes is not allowed. Downvoting a lot of posts from a specific user is prohibited just like creating sock puppets and using them to upvote your own posts.</p>

<p>In this specific case there is no indication that any user is targeting you specifically with downvotes.</p>
