Probably not too bad on a short hop, but longer flights?
It predates most of our members, but Disneyland once had coin-operated toilets. Local sanitation required that at least one stall in each restroom be free of charge. To get around it, someone would use a coin-operated stall, then hold the door open for the next person in line. Disney eventually got the message about 10 years or so into operation of Disneyland and eliminated the charge.