Your friend should check the lease regarding "house guests" and visitors. If the owner feels like you are living at the property ( if that is a violation of the lease) then the owner might serve your friend, the tenant, a 3-day-notice to cure or quit. The rules vary from city-to city and different leases prohibit different things.
If an owner or a neighboring tenant feels threatened or is suspicious of any illegal activity by anyone at the property (a daily visitor, a neighbor, etc..) then they can always call the police. It will be up to the police whether or not an arrest takes place, not the owner or neighbor.
Jessica M. Acker
Wellman Realty Company
Wellman Property Management, Inc.
Direct (310) 828-3132
DRE License # 01894323
My friend is an attorney if you need one, link below.