Zac Efron -- What I Want You To Believe About My Broken Jaw

Zac Efron has taken a page out of Alec Baldwin's playbook ... when something bad happens, turn it into a joke and people will laugh.

That's exactly what Zac is doing -- without saying a word in a new video that makes fun of how he broke his jaw last month.

As TMZ previously reported ... Zac claims he slipped in a puddle of water at his Hollywood Hills home. His jaw broke and he gashed his face.

As you know .... Zac has been to rehab twice this year for cocaine abuse.