Members can only be 13% of a "victim's" downvotes. If you try to exceed that, your downvote is rejected and not counted. Neither on the post's downvote count, nor on the member's downvote total.
So if Mary has received 100 downvotes, John can only downvote her 13 times before being limited by the system. If Mary is truly that bad, she will get downvotes from other users as well, and will eventually reach 150 downvotes, which means John can give her a TOTAL of 19 downvotes.
So the moral of the story -- if you get a message that you've hit the downvote limit:
1. Enter into yourself. Why do YOU and YOU ALONE have such a problem with this user? It's only you. If it weren't subjective and personal, other users would see the same "problem" and downvote this user as well.
2. Pray for your enemy (or enemies), as Christ did.
3. Wait a few days before attempting to "smash" your "enemy" again. You might as well: more downvotes don't come in that quickly. You're just wasting your time, and will keep getting the "You've Hit the Downvote Limit for This User" error message.
4. And for the love of humanity, don't try repeatedly to downvote your enemy after getting the limit error message! Things aren't going to change that quickly! You know the definition of insanity: Trying the same thing over and over, expecting different results.
When someone hits the limit, it sends me a e-mail message. This helps me keep in touch with the forum membership and its cliques (as well as feuds), which is useful information as Moderator. I've seen a user try to downvote User A (3) times, and User B (5) times! Someone was in a bad mood that day.