But the flight attendants sure can.

I've been on several flights where the curtain was in the wrong position. In two instances an entire row of J pax had ended up behind the curtain, which was then promptly moved back. Matter of seconds.

On another flight a single J pax had somehow ended up in the first row behind the curtain, the others were all coach pax. The purser told him there was nothing she could do, and that she could not provide J service in coach. Once in flight he was served a J meal anyway, though.

Johan