From my profile: https://stackoverflow.com/users/604511/aitchnyu?tab=reputation
-2 5 hours ago downvote Solr: best ... -2 5 hours ago downvote Solr More ... -2 5 hours ago downvote Ranking or ...
It seems personal. And he is unfortunately encouraged by SO's vote-anonymity, and AFAIK escape any consequences.
Who do I report this to, a moderator, to investigate this? Does SE have measures (human or bot) to counter behavior like this?