Dakota couldn't agree more. If it is during the Y trolley service on the A321 then I suppose it is understandable for someone in the first few rows of Y. But as soon as one person gets away with it the rest follow (presumably those unfamiliar with the plane feel safer heading to where they can actually see one rather than venturing back. KLM handles this rather well, with a polite notice hung from the curtain pointing out the toilets are in the rear. On ARN-EDI a few weeks back I saw an SK purser send someone back into Y even though there was absolutely no-one in C except a positioning pilot. Tough, but fair. ^