Here is a good prank: Sewing your sleeping friend to a couch so he wakes up to discover he’s the first cushion-based Transformer. Here is a not good prank: Sharing a picture of your classmates over social media with the caption “Planning the school shooting 😊😊😊.”

The latter, however, is just what one Arizona high schooler did via Snapchat this week, delighting students and faculty alike. Just kidding, he got locked up. From NBC News:

Phoenix police arrested the teen, who admitted involvement in the incident but told officers it was a prank, according to the statement.

The student was detained for one count of creating a hoax, a class 4 felony, according to the statement.

“I didn’t know and I didn’t want to assume it was a joke,” the student who reported the image to police told KUSA, “because if I would have woken up today and seen that he really did shoot up a school, I know how bad I would have felt if I knew I could possibly have stopped it.”

In general, if your gag leaves people with the impression they can prevent a terrible tragedy, it’s probably time to go back to toilet paper and eggs.

[Image via KPNX]