I am sure this has been mentioned already but...........Y passengers using the J lavatory.
Most of the 737's have the cabin divider / curtain - yes they are ugly but they serve a purpose. On the reconfigured 737's, there is no divider at all. Despite the verbal instruction from the CSM, economy passengers think the J lavatory is available to them. The curtain was a detractor - yes it looks terrible but it stopped economy passengers walking up there.
I just flew back from CNS in Y and watched about 6 Y passengers walk up to that lav. I felt bad for the J passengers who then had to wait.
Either bring back the curtain or the crew need to tell Y passengers to using the toilet in the back, unless it is an emergency case (we know what that means).