trope: Oh you wacky kids with your hi-jinks and your pranks

“You say you found a corpse of a thirteen year old girl on the beach? Oh, you’re just pulling my leg.”

When the protagonist experiences something genuinely frightening, such as finding a corpse, or that someone has been in their room while they were home alone, and it is treated as an attention-seeking prank.

Or, when something is done that is written off as a prank or a joke, but is actually pretty damned spiteful.