If you wanted to get the post deleted, you could try contacting the person through the forums, comments(not a good method) or if someone had the users e-mail or other contact information and telling them the proper way that to get deleted. Because as was stated you cannot have them deleted yourself.
Also related, How Can I delete my Account
The best way to do this is tell the person that they have to reach out to the Staff through a Contact Form and showing them the info needed to be deleted. But as was stated in the comments it may be better for other users if the account stays un-deleted, as that means votes and other contributions may be deleted as well. Meaning that other users may lose rep.
The person may always change their mind about the deletion.