Not sure if it is true, but on UA they always say that FAA regulations do not allow you to move between your ticket cabin or some such thing. The point is that Y's going towards J is viewed as going towards the cockpit.

A while back on AC I was in a plane where J was 100% empty and I was in the front row of Y and went towards the front washroom, because it was closer. I guess I moved too quickly as the FA got concerned that I was approaching the cockpit. She was fine when I told her where I was going.