We do not tolerate the harassment of people on our site, nor do we tolerate communities dedicated to fostering harassing behavior.
Harassment on Reddit is defined as systematic and/or continued actions to torment or demean someone in a way that would make a reasonable person conclude that reddit is not a safe platform to express their ideas or participate in the conversation, or fear for their safety or the safety of those around them.
Being annoying, vote brigading, or participating in a heated argument is not harassment, but following an individual or group of users, online or off, to the point where they no longer feel that it's safe to post online or are in fear of their real life safety is.