Can I put roller blades into a bag and fly with it as my cabin baggage with Ryanair?
There were no problems with roller blades at the airports.
With rare exception, airlines do not have any specific rules as to what can and can't be carried on board a flight - they leave those decisions up to the various airport security organizations, so the exact answer for this question will really depend on the airports/countries you're flying out of. The airline will of course enforce maximum sizes and weights, so you'll need to keep within those.
Although not directly relevant (as RyanAir don't fly to the US), the USA TSA does allow Roller Skates (and thus one would presume, roller blades) to be take in carry-on luggage. Surprisingly (to me, at least) even Ice Skates are allowed in carry-on baggage.
I would be surprised if any country did not allow roller blades to be taken on board - but you may want to check with the relevant airport security for the airport you are flying out of in advance to be 100% sure.
From about twenty years ago up until five or six years ago I always used to travel with my rollerblades. Originally I always took them as cabin baggage.
But after 9/11 the airlines started to tell me I couldn't bring them on and I had to check them in as baggage. I seem to recall one person pointing out that I could unbolt the wheels and use the metal frame edge as a terrorist weapon.
Obviously this kind of thing is going to be open to interpretation from airline to airline and possibly even staff member to staff member.
I have never flown with RyanAir though.