Zac Efron Extra Fired From 'Neighbors 2' After Posting Fake Weed Pic

Zac Efron is sober ... and if you say otherwise, you could lose your job.

An extra on “Neighbors 2” learned that lesson the hard way this week, after he Instagrammed a pic from the set showing a baggie filled with fake weed, with the caption, "Thanks for the weed Zac Efron! BTW it's only a prop, people."

Apparently the disclaimer wasn't enough. The extra was 86'd almost immediately. Our source says it wasn't the first time the extra had gotten in trouble for inappropriate posts.

We're told Zac was not involved in the decision to fire the guy.

Efron went to rehab in 2013, so it's a sensitive subject.