My grandma was in economy class on a full Air Canada flight. The bathrooms were, unusually, very occupied, and were accompanied by long lines and passengers waiting. They soon became filthy; she saw egesta on the floor and toilet in some of them. She asked the cabin crew if the bathrooms would be cleaned, but they just put paper towels to hide the egesta without cleaning.
So without asking first or explicit permission, she walked up to use the business class lavatory, where the Service Director chided her:
Madam, use the lavatories in Economy. Please refrain from using the lavatories up here.
My grandma apologized, and tried to explain the long waits and the filthiness, but he still chided her the second time:
I already told you not to use this class's lavatory.
In such unusual cases of filthiness and unavailability, can economy-class passengers use business-class toilets?
I ask this for reputable airlines in general. American Airlines permits this gambit, but other airlines' stance is unclear. If Air Canada loathed this, why'd they compensate this grandma?