Legal Question in Real Estate Law in California

I assume that by "landlord" you mean a true landlord and not just a cotenant of the "roommate" who happens to be somewhat senior in role due to being "on the lease" or otherwise in charge of the situation. I'd start out by saying that the rights and duties of landlords and tenants are rather well defined in the law, after centuries of landlord-tenant disputes covering every imaginable kind of hassle from whether the rent may be paid with a sackful of pennies to whether murder terminates the lease. I would say that, first of all, "acting irrational" is a very broad and very subjective condition, and probably 99% of the time would not impact the landlord-tenant legal relationship, at least not to the extent of justifying removal of belongings and a lock-out. Next, I'd say the same about threatening lawsuits. It's an exercise of free speech, and does not in and of itself affect the rights of the tenant (or the landlord) under a lease or rental agreement. Finally, failure to pay rent IS (almost always, anyway) a breach of the lease or rental agreement, and the express terms thereof, limited by statutory rules governing nonpayment of rent, termination of the lease or agreement, and then eviction, will govern what may happen thereafter. Generally speaking, the breaching tenant is entitled to notice and an opportunity thereafter to pay up before being subject to termination and then eviction. There are somewhat complex laws governing all of this, set forth in the Civil Code (sections 1940-1954 and 1980-1991 covering landlord-tenant relations ) and Code of Civil Procedure (sections 1159-1179a covering eviction), but for a non-lawyer landlord or tenant I strongly recommend self-help legal guides such as the large-format paperback books published by firms such as Nolo Press with titles such as "How to be a Landlord in California" or "Tenants' Rights in California." If you buy a book like this, be sure it is written based on California law, not some other state.