First there was David O. Russell's much-publicized on-set freak out, and then it was Christian Bale all but tearing a cinematographer in half. Now a video has surfaced featuring Matt Damon directing Adrian Grenier in what looks to be a PSA for a site called One by One, which does exist and (thanks to commenter Corey for pointing this out) is apparently an organization that helps children in poverty from around the world. Matt Damon is the company's spokesperson.

So Grenier has, like, five lines to deliver, but he keeps stumbling over his words and pissing Damon off. Meanwhile, Jeremy Piven (who looks like he's either in his full-on Ari Gold character or just stepped off the set of Entourage) is frantically pacing behind Damon as he continually corrects and eventually goes off on Grenier. Piven doesn't say a word, so it's tough to say, yes, he is in character as Ari Gold -- though he does look to be acting as if he were Grenier's agent. That being said, Damon refers to Grenier by his real name and not Vince (though at one point Grenier asks if he should talk as Vince), so who knows what the hell is going on here.

I personally think they're filming something for an upcoming Entourage episode and decided to have a little fun at the same time by throwing together this little viral video. Either way it's pretty hilarious, and I wish it went on a drop longer so we could really watch cameo king Matt Damon freak out hardcore.

Watch the NSFW, foul-mouthed video after the jump, and you decide: is it real or is it fake?