I've sat near the back of J close to the PE section in K seats, and when I needed the lav I went forward and cut through the galley. I'd never cut through where people are seated, which is just rude. Mind you that was a 77G. And that learned, I now get a seat in A vs. K.

Looking at the 77A seat maps it's a hike back to row 46 to find a galley to cut through. Just how much room is there in front of 30 D-G? On CX's own seat maps the amount of room looks huge vs. a 77G so maybe it's not so rude. Still I can't imagine having commuters back and forth for a dozen hours.

I bet the people in row 39 have the same problem only right to left for the biffy.