(v) the act of being bad at the sex.
Origins come from the fact that most people called cyril have a loose, at best, understanding of the general rules of sexual intercouse. A cyril is someone who lures you in and proves to be not only useless but overconfident and somtimes, inadequately groomed.
Cyril is also a male human name, not all men named Cyril are crap roots. However some are, and they are especially aggressive during threesomes. It often takes a lot of showering to wash the cyril off.
Girl I know, I can't believe we got cyrilled, it was like it was his first time.