A little background first...
We have been bringing our son Tom to the matches with us the past 2 seasons - he turned 21 months this week, so that's pretty much as many games as possible in his short life! We usually sit in 124, and therefore use the facilities in the west concourse, including the family washroom right across from 123 when Tom needs to be changed. In our experience, it's generally families using that room - sometimes parents like us needing the change table, often moms with sons or fathers with daughters where it's difficult to use the main facility, and sometimes just a parent with multiple kids that are hard to wrangle by going into the main facilities.
For last night's friendly, we sat in 116 - to digress, I was willing to attend for $30 a ticket, but not $112. Anyway, Tom needed a change at the half, and a very different experience for the family washroom behind 116. There were already a couple people in line when we got out to the concourse, and after the first guy wouldn't let us in, the second was gracious enough to let us go ahead of him... I did guilt him a little with a 'come on, it the family washroom', but he seemed like a nice guy and I'll give him the benefit of the doubt that he would have anyway. Later (still during the break) I had to go myself and queued up around 114/115, and was in and out pretty quickly, even though the line was pretty long... when I came back to my seats, there was a 7 person queue for the family, and only 1 guy (who looked about 80) seemed to actually need it.
So after all that, I'm wondering what the general etiquette is? It seems to me that priority should be to the people for whom it's designed / those who actually need it the most. If a guy wheeled into the mens room and needed the handi stall, people would certainly let him take it as soon as available and not say 'tough shit, wait your turn in line like everyone else and hopefully the 1 space you can use is free when you get to the front of the line'.
To note, I think you would still get to use a urinal faster is you stood in a 30-person line for the regular mens room than you would being 5th in line for the single-serve family facility, so I'm wondering if it's laziness, or something else, that compels people to queue for the family.