To be fair, it's probably worth registering and then offering it to the original owner at cost to prevent a more malicious user from holding it hostage.
My intention is for it to be returned, whilst also sharing an entertaining, and educational message with the community. Don't let your domain names expire otherwise anyone can have them. ¯\_(ツ)_/¯
Eh, that’s exactly what I’d do. Register it, get a LOL out of it, then hand it over. I’d even give it to them for free. It’s funny and it’s harmless and teaches them a lesson with some mild embarrassment.