With the rep system, users with a certain amount of posts can give other users positive and negative rep. Regular members can only do this once to a single member every three hours, to prevent someone from increasing or decreasing one person's rep to a large degree. When first implemented on RMRK, only the sum number was displayed, instead of both positive and negative values.
Super Moderators and higher, not limited to the 3 hour wait period, are able to give positive and negative rep as much as they want, while admins have the ability to edit it to a specific number. They have been known to do this on a scale of hundreds, and even thousands.
Caring too much about rep
Throughout RMRK's history, countless people have been accused of caring too much about rep. When a member mentions or complains about their negative rep, they are usually ridiculed and though less of by others. Whether or not a person's rep matters is open to debate, but the general consensus amongst long time members is, it doesn't. It's been both used legitimately and not. If a user's negative rep reflects that they're legitimately disliked, then they shouldn't complain about it, but instead find out what they're doing wrong and try to better themselves.