Sentence:  I knew I had to be very careful when I was crafting the story, so that it wouldn't be a <WSD>Scooby Doo</WSD> moment&mdash;you know, the one where the villain rips off his mask and tells you why he did it&mdash;and that he would have gotten away with it, if not for those pesky kids! 
Meaning of the word marked with <WSD> tags:  An American cartoon franchise, named for one of the main characters, a large dog, and featuring as protagonists four "meddling" teenagers who would unravel seemingly supernatural mysteries.