Troll
Overview
Trolling (or troll, for the person who does it) refers to deliberately provoking a community or an individual and enjoying the anger and chaos it causes. The term was born out of message board culture, and it happens anywhere users can post: social media, comment sections, chats, question boxes, and more. The goal of a troll isn't constructive discussion. It's getting an emotional reaction out of the other person.
How trolls work in question boxes
Trolls in question boxes have typical patterns. Meaningless strings of characters and the same question sent over and over are simple trolling, and rate limiting can cut down on them. A cleverer trick is to provoke with a question disguised as a normal one. A question like "Which do you like better, X or Y?" creates a situation where you get criticized whichever you choose.
Questions that stir up emotions are another standard trolling tactic. The troll sends a question that touches on the owner's insecurities or past failures, trying to draw out a shaken answer. If you handle it calmly, the troll tends to get bored and leave, but if you react emotionally, they may decide "it's getting to them" and escalate the attacks.
How to deal with trolls
A well-known saying about dealing with trolls is "Don't feed the troll." A troll's goal is to get a reaction, so if you don't react, the goal isn't achieved, and the troll may lose interest and leave.
In practice, delete a troll's question as soon as you read it. Don't answer it, don't mention it on social media, and don't tell your followers about it. Ignoring the troll is the basic way to deal with it. Sharing it as "Look what question I got" gives the troll attention and also risks inspiring copycats.
Telling trolling apart from fair criticism
Not every negative question is trolling. It's important to tell fair criticism and frank opinions apart from trolling. The key is "whether it's constructive." "I think your answer is wrong about X" is criticism, while "Your answers are boring" is trolling.
Face criticism sincerely, and ignore trolling. Being able to tell them apart may make running your question box easier. When you're not sure, use as your standard whether answering that question has value for you or your followers. If it has no value, you can ignore it, whether it's trolling or not.