Aside from Y pax just being deliberately awkward (a trait not unique to Y), shouldn't the beef be with the airlines who fail to provide adequate facilities in Y, not the Y pax who need to go ?
The loo to seat ratio on LH Y is a disgrace, (and also have a thought for the unfortunate Y's who get stuck with a seat near the loos). Not only is it uncomfortable for those queueing or sat near the loos, but the level of use on an 8 hour plus flight leads to a very unpleasant/potentially unhygenic situation. Moreover, everytime there is a turbulence incident reported here on Pprune, there is a race to attack the idiots not wearing their seatbelts, only to be followed by more objective comments that the level of injuries equates to the number of people who would normally be queueing for the loo at that time of the flight.
As a generally rule compliant individual, if I was in Y needing to go, and there was a 20min Q for the Y loos, on safety grounds alone I would consider it appropriate that I have access to the J loo to minimise the turbulence risk, never mind the biological one!