A FlyerTalk Posting Legend
Join Date: Sep 2002
Location: LAX/TPE
Programs: United 1K, JAL Sapphire, SPG Lifetime Platinum, National Executive Elite, Hertz PC, Avis PC
Posts: 42,431
Bottom line - anyone who experiences this should file a complaint. Unless there is a published policy that regulates priority or restricted access to the lavatory, no crew member has any right to restrict the lavatory for their own personal use. File the complaints, and when encountered on board, just unlock the lavatory yourself if you see this happen.
What are they going to do, divert the flight? Dare them to. I doubt HQ would be impressed with that decision.