How to remove your MyAnimelist.net account
You can’t delete your account. Use the tip below to obfuscate your personal data.
There used to be a way to remove all your lists in one go, but due to perfomance reasons this option is removed. So you have to do it by hand.
More info can be found here: http://myanimelist.net/forum/?topicid=298846#msg10792692
Helpful Trick: Obfuscate your profile info.
Because most accounts and profiles at MyAnimelist.net cannot be removed, we suggest you login and change your account and profile information altogether.
Make sure you are logged in to your account on the site and click on the profile or options settings. Locate the fields with your personal info (email, name, address) and fill in generic, random information instead. If you can only select from several fields, change anything personally identifying. If possible, use a homepage/URL field or long text field (such as Description) and put this line in it: http://remove.org/removal-requested. This may encourage webmasters and admins to create an easier removal outlet.
Helpful Trick: Removing online data
Helpful Trick: Remove third-party logins
If you signed up for MyAnimelist.net using a third-party login such as Facebook or Twitter, you probably want to revoke all access from MyAnimelist.net. Click here to find out how.