No one deserves to be harassed, including on Reddit.
Moderators can take care of harassing comments or posts on the subreddit itself, but we cannot take action on things elsewhere: This includes harassing private messages (sometimes referred to as DMs since Twitter and other sites use the term “direct messages”). It also includes posts on other subs directing people to attack your post, comment, or person. We know it happens, and it's unfortunate.
What should you do if you're receiving them? You can block them, but you can report them to the admins. The admins have the ability to take action on those who do it.
Here's a quick run-down of how to take action if you are subject to any
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