A scuba diver who was a CBer stopped at the top of a low cliff, he thought safely far from a nearby inshore fishing villages whose inhabitants did not like scuba divers coming around. He kitted up and then said into his car's CB: "This is Scooby-Doo going down." (i.e. "going off the air").
He climbed down an access ladder fixed to the face of the cliff, to the sea, and thought "This is Scooby-Doo going down.".
In the sea he swam down to the seabed to take shellfish and thought "This is Scooby-Doo going down."
Something had seen or detected this, and the fishing village's 40-foot dredger-submarine went to the place and summarily shovelled him up and logged "This is Scooby-Doo going down.".