How to delete a Gravatar account?
The description of the service:
Gravatar a portmanteau of globally recognized avatar is a service for providing globally unique avatars. On Gravatar, users can register an account based on their email address, and upload a digital avatar to be associated with the account. Gravatar plugins are available for popular blogging software; when the user posts a comment on such a blog that requires an email address, the blogging software checks whether that email address has an associated avatar at Gravatar.
Deletion complexity:
Not possible
You can't delete your Gravatar Account without deleting your entire WordPress Account.