There are some very immature people on this site that will down-vote me if I don't choose their answer. Has anyone else had this problem?
This is something you can't actually prove, so it's just an assumption.
P.S. If you don't accept this answer, I'll down vote you.
If it becomes blatant, there are reputation recalculation algorithms that are run on an undisclosed and perhaps not consistent schedule that will adjust for it. I they are being clearly abusive, flag the abusive comment/answer and explain the situation in the flag text box and a moderator will look at it.
People are down-voting over inane reasons!
News at eleven.
People downvote for a number of reasons, not necessarily logical. They also upvote for the same not necessarily logical reasons.
I think that in the end it evens out.
Also there is no way to know intent of a vote, not until
SO Neural Iterface 0.3.2 goes public Beta in about 6 to 8 weeks.
I don't think a single occurrence of this is very provable or worthy of being searched for and reversed. However, if there are users who are consistently doing this, I would hope the fraud prevention algorithm does or will look for this and reverse it. It is not a behavior that seems in keeping with the spirit of SO.
If you sincerely have a problem, send an e-mail to firstname.lastname@example.org. However before doing that flag the questions/answers you believe this has happened on and why. The moderators will then investigate if necessary.
However the voting mechanism does get checked by regular scripts that will undo common down-voting scenarios.
While there are those who may partake in this behavior, I believe they are in the minority and a single downvote does not carry enough weight to really have a detrimental impact on your reputation. In addition, if they go on a campaign of retributal downvoting, they will get caught out by the system detecting their unsportsmanlike conduct.
I've had this problem, but I can't prove it.