Under California law^[24] a vexatious litigant is someone who does any of the following, most of which require that the litigant be proceeding pro se, i.e., representing himself:

1. In the immediately preceding seven-year period has commenced, prosecuted, or maintained in propria persona at least five litigations other than in a small claims court that have been (i) finally determined adversely to the person or (ii) unjustifiably permitted to remain pending at least two years without having been brought to trial or hearing.
2. After a litigation has been finally determined against the person, repeatedly relitigates or attempts to relitigate, in propria persona, either (i) the validity of the determination against the same defendant or defendants as to whom the litigation was finally determined or (ii) the cause of action, claim, controversy, or any of the issues of fact or law, determined or concluded by the final determination against the same defendant or defendants as to whom the litigation was finally determined.
3. In any litigation while acting in propria persona, repeatedly files unmeritorious motions, pleadings, or other papers, conducts unnecessary discovery, or engages in other tactics that are frivolous or solely intended to cause unnecessary delay.
4. Has previously been declared to be a vexatious litigant by any state or federal court of record in any action or proceeding based upon the same or substantially similar facts, transaction, or occurrence.

Appeals of an existing action do not count as “final determinations”. Appeals and writs that are related to a current action do not count as “final determinations” or additional determinations, because until all avenues of appeal have been exhausted the determinations cannot be construed as “final”.^[25] A judgment is final for all purposes when all avenues for direct review have been exhausted.^[26] Interlocutory decisions before a judgment cannot be considered “final determinations”.^[27] Docket lists show nothing about qualifying merit of interim motions (Id.)

To meet the unspecified criteria for "repeated" motions or litigations, the number must be much more than two, and the rule based on case law seems to be around 12. "While there is no bright line rule as to what constitutes “repeatedly,” most cases affirming the vexatious litigant designation involve situations where litigants have filed dozens of motions either during the pendency of an action or relating to the same judgment." ^[28]

Repeated motions must be "so devoid of merit and be so frivolous that they can be described as a flagrant abuse of the system, have no reasonable probability of success, lack reasonable or probable cause or excuse, and are clearly meant to abuse the processes of the courts and to harass the adverse party than other litigants."^[29] Evidence that a litigant is a frequent plaintiff or defendant alone is insufficient to support a vexatious litigant designation.^[30] The moving party, in addition to demonstrating that the plaintiff is vexatious, must make an affirmative showing based on evidence that the case has little chance of prevailing on the merits. If the plaintiff is so determined, a bond may be required, and if the bond requirement is not met within a specified time period, a judgment of dismissal is ordered. A finding of vexatiousness is not an appealable order, but a dismissal for failure to post a bond requirement based on a judgment of vexatiousness is appealable.

Habeas petitions do not count towards vexatious litigant determination.^[31] Vexatiousness in Probate Actions are governed by a different standard (Cal. Prob. Code s. 1611).