Say the boundary in operational terms
Name the contact, behavior, topic, access, or commitment you will and will not participate in. For a message about how to apologize for deleting shared digital files, use this factual base: name the post, message, file, audience, and privacy impact as precisely as possible.
Define any necessary exception
If an exception is necessary, give it one purpose, one channel, and a clear limit. Delete or correct what you control, notify affected people, and preserve evidence needed for a formal response. Make the immediate next step clear enough that the recipient can answer without reconstructing the entire history.
Respond to escalation safely
Do not repost the harmful material inside the apology or blame the platform for your choice. Escalate intimate images, impersonation, account compromise, threats, and personal data exposure through platform and legal safety channels. You do not need the other person to agree with a boundary for you to follow it consistently.