As long as you make a prank video out of spoiling things, you should be good:
Edit: Looks like I messed up the link. Was trying to link to an exact time in the video. Basically it's a dude driving along with a megaphone spoiling the release of a Harry Potter book to a bunch of people waiting in line outside of a bookstore. It's at 1:23 here:
https://www.youtube.com/watch?v=iL5NltsDWX8