A phrase used when you wish to trick another into believing that someone (fictional or otherwise) is dead, when they really are not. Derived from the conclusion of Harry Potter's 7th installment, in which the author declares in so many words,
"Hey guys, our Hero is dead!!
...jk I fooled ya'all :)"
Tom: Dude last night your mom had a stroke after I was through with her.
Tom: Don't worry man! JK Rowling!