The only time I EVER, EVER have a problem with airlines in Re to the coach/first class issue is when the bathrooms in coach are inaccessible, for whatever reason (food carts, broken, long long lines). If someone has to go to the bathroom very badly (many reasons come to mind), then it is appropriate to allow that person to use whichever bathroom is available. In most cases, I have seen the airline do this- but in those instances where the airline insists that passengers, under all circumstances, use the bathroom in their cabin, I have a problem.