My biggest AC complaint (yes biggest) is lack of enforcement for J bathrooms being for only J pax. I once flew J Yyz to lhr and saw a ton of Y pax (including small children with parents) using the washrooms. At one point a lineup of 3 J pax were waiting for the bathroom. One Y pax came out finally and lets just say the bathrooms toilet was no longer useable for the duration of the flight.

A simple annoucement after takeoff will solve a lot of this problem. "There are 4 bahrooms a the back if the plane for economy passengers and 3 at the front for Busness passengers". Many airlines do this and have far less issues with the lavatories.