DCC is avoidable...
You can avoid the DCC but the option to do this is well hidden. After you enter your card number there are changes on the screen. If you click the more information option somewhere around the amount a popup screen launches where you can deselect the DCC.
Booking Ryanair flights about 10 times a year I still got caught out by this a month ago ending up overcharge by appr 10 GBP...