Has an unauthorized civilian ever tried to land on an aircraft carrier?
I'm not exactly sure whether this counts, but I think the landing of South Vietnamese Air Force Major Buang-Ly on USS midway using a Cessna O-1 Bird_Dog comes pretty close.

Though Major Buang-Ly was not a civilian, he has never seen a carrier before and the landing wasn't exactly illegal. It was permitted by Captain Larry Chambers during Operation Frequent Wind, who even scuttled helicopters on the deck to ensure safe landing.

The image below shows the aircraft as it comes to a stop.



Image from forum.worldofwarships.com