What is Scooby-doo Effect?
1.
The act of the villain telling the audience (be it in a TV show, novel or play) the crafty ins-and-outs of his or her plans, more often than not after they have been caught out or caught in the act.
More often than not this relates to the exact moment that the rest of the characters learn about what exactly has been going on.
"So that was my plan: to steal the plans for the new Multi-Storey car park from the Town Hall so it could never ever be built.
And I would've gotten away with it too if it weren't for you meddling kids!"
The Scooby-Doo Effect in action.
See