I've noticed on a recent JFK-NRT flight, the FAs decided to usurp the large toilet for their exclusive use-- leading to sometimes long lines of waiting passengers waiting to use the remaining toilets.

Absurd that customers should wait needlessly.

I also noticed that to counteract this customer-unfriendly act, one of the civic minded passengers would every so often arise from his/her seat to unlock the locked "employee" toilet so that others could use it.