"But train stations don't travel at 30,000 feet in a cramped metal tube with filtered air," Seaney said. "Let's face it, lavatories on planes are not frills; we are talking basic human needs here and for Ryanair to talk about removing some lavatories while making passengers pay for the remaining toilet, at least for Americans, doesn't even pass the giggle test."
Ray Neidl, an independent airline analyst, generally supports airlines adding on extra fees.
The latest example of a new fee came last week when Spirit Airlines announced it was starting to charge a fee for carry-on bags, a fee higher than that to check luggage.
But for Neidl, Ryanair's bathroom fee is "probably stepping over the line."
"I've been always been an advocate for charging for different services on flights, but that one is going a little too far, that and withholding water," Neidl said. "Everything else is on the table."
Passengers can always revolt, although he said if any airline could get away with this, it would be Ryanair.
Ryanair is notorious for its fees. While most airlines now have checked-bag fees and charges for changing your flights, Ryanair was a pioneer in those fees and adding additional ones, such as charging all customers extra to check in for their flight. And that's not even in the airport, that's online.
Travelers put up with these fees because the no-thrills airline typically offers ridiculously low airfares on short hops between European cities.
"With Ryanair, you can never tell. I don't think it is going to work anywhere else but with Ryanair, it could work," he said. "Bottom line: I still predict it doesn't happen."