Cal. Prob. Code § 1611

If a person files a petition for visitation, termination of the guardianship, or instruction to the guardian that is unmeritorious, or intended to harass or annoy the guardian, and the person has previously filed pleadings in the guardianship proceedings that were unmeritorious, or intended to harass or annoy the guardian, this petition shall be grounds for the court to determine that the person is a vexatious litigant for the purposes of Title 3a (commencing with Section 391) of Part 2 of the Code of Civil Procedure. For these purposes, the term “new litigation” shall include petitions for visitation, termination of the guardianship, or instruction to the guardian.