You're the bully is a silencing tactic sometimes used against people making complaints. Like You're the sexist, it attempts to turn around accusations of bad behaviour on the person who was originally the victim of it.
"You're the bully" relies on the recently increased awareness of bullying, especially online bullying, as an issue. It characterises any negative online attention as bullying.
However, bullying is about power, and is generally understood to be something that occurs when people with more power exert it over those with less. The stereotypical schoolyard bully is a large, physically strong kid who picks on smaller, weaker ones. Bullying can also occur on other axes of power and oppression. For instance, people who are members of marginalised groups (LGBT people, people with disabilities, people of racial minorities) are often bullied by those not in those groups.
"You're the bully" is sometimes used against, for instance, an individual or group of individuals campaigning against a corporation, a conference attendee complaining about a speaker, or a member of a marginalised group standing up for themselves in the face of discrimination.
"You're the bully" is also a form of Tone argument, in that it is often used to criticise the forceful nature of someone's statements and to imply that the complainant(s) should have been less assertive.
"You're the bully" can be said against the target of an investigation when the target becomes aware that she is being investigated. Anyone suspected of tipping her off about the investigation risks being charged with obstruction of justice, even if she is innocent, so she is accused of having power over others and abusing it just by being aware. In cases where the law enforcement officers are harassing the target, she may be labelled a bully, "too smart for her own good," or "too paranoid," to bring attention away from the harassment.
Victim-blaming or concern trolling statements can involve
- Quit backpacking to so many third world countries, you'll just arouse more suspicion. (Denial of agency.)
- Curiosity killed the cat.
- You talking about this is making me paranoid, stop stressing me out.
- Isn't that personal information? Are you sure you should be talking so openly about this?
- If you keep trying to find out who's doing this, they'll keep harassing you more.
- You're dealing with professionals, don't fight back.
- Maybe someone just has a crush on you.
- You're crazy.
- If you tell one more person about this, you will die in torment.
- Forgive me.
One can be accused of being a bully just by virtue of being curious. For example, what at first seemed like a random anonymous Internet troll suddenly starts spewing private information that they would have only known had they hacked into the victim's computer. Then when the victim crosses borders into another country, she finds that real people offline approach her and drop hints about her private information. Upon returning with her discovery, she is labeled a bully.