Legal Question in Landlord & Tenant Law in California

What is the activity and/or requests that are unreasonable? My gut response even absent more facts is, either the landlord can resolve it if it is harassment that breaches the lease agreement inclusive of the implied duty to let the other tenants enjoy their tenancies by sending a notice to the "harassing" party that they are violating their lease agreement... Otherwise, it would be a police matter or something the harassed tenant needs to resolve with their own use of civil process.