My experience with the "no congregating" rule shows that hanging out around the front lav in the cabin door area is the "no-no" and rigorously enforced by the FAs. Reckon ya can figure this out by yourselves. I see plenty of congregating at the rear lavs with nothing more than watchfulness by the cabin crew.
Yes, this is one pax that goes on high alert when someone walks to the forward lav ! Especially when that someone tries to come from the rear cabin .......