A Texas teen has been jailed since late March for what his father says was just a dumb joke he posted on Facebook.

Justin Carter, then 18, and a friend were arguing with a third person about the online video game League of Legends, when Justin made an offhand comment about shooting up a school.

"Someone had said something to the effect of 'Oh you're insane, you're crazy, you're messed up in the head,’ to which he replied 'Oh yeah, I'm real messed up in the head, I'm going to go shoot up a school full of kids and eat their still, beating hearts,'" recalled Justin's dad Jack. "The next two lines were lol and jk."

But an unidentified woman in Canada who saw Justin's comment didn't realize it was supposed to be tongue in cheek, and tracked down the teen's address using Google.

After noticing that he happened to live near an elementary school, the "concerned citizen" immediately called the cops.

Justin was subsequently arrested and charged with making a terroristic threat — a crime punishable by up to eight years in prison.

"These people are serious. They really want my son to go away to jail for a sarcastic comment that he made," Jack told KVUE.

A search of Justin's Austin home turned up no weapons.

The teen's family has since started a petition to raise awareness of his predicament, and call for a thorough review of terroristic threat laws.

"Justin was the kind of kid who didn't read the newspaper. He didn't watch television. He wasn't aware of current events," said Jack. "These kids, they don't realize what they're doing. They don't understand the implications. They don't understand public space."

[H/T: Opposing Views, screengrab via KVUE]