By definition serial down-voting applies to a window of time in which a number of down-votes are directed to the same individual. Today I'm seeing a particular user (whom it isn't particularly relevant to identify) come through the Low Quality Post review queue with several one-liners. Some I can legitimately vote for deletion, but I tend to give the benefit of the doubt when an Answer can be construed as a genuine attempt to Answer.
When I cannot bring myself to vote for deletion, I may down vote such posts because they are simply wrong or so incomplete as not to be helpful unless the Reader were to know enough about the problem to do without the brief hint. (This is of course a judgement call...)
Now we come to my point. When a particular user keeps showing up in said review queues, my down-voting will quickly begin to satisfy the automated criteria for serial down-voting. I do not care so much for the stain this might cast on my reputation (ha!) as for the fact that I would be wasting my time in trying to delineate between junk one-liners and churlish but legitimate attempts to Answer.
Is there perhaps a precedent for flagging for Moderator attention? I did a meta site search for something on this topic but came up dry. It seems to me these Posts are in the Low Quality review queue in some cases because they've already been manually flagged (though many, perhaps most are there out of automated searches that flag one-liners).
Moderator attention is a valuable/scarce commodity, but I think recognizing a systematic behavior by a User may be called for in this situation. Of course it might be redundant if a higher-order search exists that Moderators see when multiple of a User's Posts go into review queues.