This is a blooper from Hardly Working: Bloopers - http://www.collegehumor.com/video:1814739
There's a lot of layers here. The joke is that Dan keeps ruining the takes of me being slapped. He was supposed to say something different here, though. For a few seconds, you can see that everyone is confused about if we're still shooting and if Dan's working to something or if he actually bloopered. It was a real blooper of Dan ruining the real shot of a staged shot for a fake blooper; so it almost canceled itself out. It's hard to explain. It blew our minds.