Any excuse
I've only used Ryanair once but that was once too often.
The web site would not accept online check-in for one of our party, so, surprise, money was needed to "re-open the booking reference". Same again on the return trip.
Ryanair treats customers as a hideous inconvenience. This doesn't have to go with the low-cost concept. When I flew with FlyBe it was a surprisingly pleasant experience.