On a 767 flight last year, EZE-IAD, I encountered a similar problem. Breakfast had been served about 2 hours before landing, and about and hour after that I needed to use the bathroom. I was seated in C and proceeded to to the business bathrooms, only to find that the port bathroom was blocked by a serving cart and the bathroom on the opposite side had a large number of Y passengers lined up to use it, and five C passengers waiting.

I waited about 10 min behind the C passengers, but there was no movement since the Y passengers just pushed their way in. I asked one of the FAs about whether the blocked bathroom had a problem, and was told no, and she was not prepared to move the cart since they needed it there.

I went back to my seat and flagged down a different FA, to ask her to ask the purser to remind the Y passengers that their bathrooms were in the rear, and also to ask for an exception that I be allowed to use an F bathroom (this was after UA on all other flights were announcing it was a UA security policy for passengers to stay in their ticketed cabin).

The FA returned from talking to the purser, and who said she would take care of the problem, but I was forbidden to use the F bathroom (F was not full). After about another 15 minutes with no announcement or resolution of the blocked bathroom or the Y passengers being directed to use the appropriate facilities, I flagged down a third FA. I explained what was going on, and told her to tell the purser that I would need to talk to one of the cockpit crew, since obviously at least some of the crew (including the purser) were incapable of following UA security directives, and were also deliberately blocking one of the C bathrooms. This 3rd FA agreed with me that the situation was intolerable and proceeded to talk to the purser.

I guess the request to talk to the cockpit jolted the purser since I was invited to use the F bathroom (but the situation with the other C passengers was not taken care of).

John