Anti-climactic, dragged on for too long, and all in all it was kind of dull and predictable. The presentation was detrimental to the overall effect, there was no real change in pacing and the joke has just been done before - "oh man, you totally misunderstood what I was saying!".
But you know, you can always improve on these things. I suggest better casting and probably looking over and rewriting the scripts you use more (or if you've got someone else to do that, just get a new writer). The shots weren't bad, but again lended to the predictability of the joke - whilst yes, it was clever to have his face hidden from the camera whilst he was facing the floor, it was instantly understandable that someone had done something to his face whilst he was sleeping in the next shot because there was no other logical reason for him to have his face turned away.
Personally, I think a better story would have been essentially the same, but the face reveal would be the moment he sits up. The conversation would then go on as planned, except this time with the use of shot-reverse-shot, and instead of having the main character ask the other guy "you tag-teamed my girlfriend whilst my sister filmed?!" he would simply get up and leave. The second friend would then reveal himself next to the original friend that showed up, and go "can't the guy take a joke?", whilst the other man replies "THIS is why I sleep with his girlfriend". Then they go back down.
That's just my idea of what would make a much better story, and it remains basically the same. I bet you would have came to a very similar approach if you'd just looked over the script a week after writing it - I tend to do that, just write a script that I think's great and then when I look back at it make so many adjustments it becomes hardly recognizable save the basic premise.
Good luck for the future!
