Okay, so, I can't personally verify that this scene was improvised, but it sure does feel like it. Plus, it was an Apatow production, so... I think it's a fair assumption that this 10-minute scene is classic Apatow-produced improv:
https://www.youtube.com/watch?v=MfJcEziJcy4
Pretty hilarious, but obviously way too long (and I'm thinking that they probably shot a lot more than the 10-minutes we see here). The theatrical-release version is comedic perfection, in my opinion:
https://www.youtube.com/watch?v=vWax13Inj4g
https://www.youtube.com/watch?v=MfJcEziJcy4
Pretty hilarious, but obviously way too long (and I'm thinking that they probably shot a lot more than the 10-minutes we see here). The theatrical-release version is comedic perfection, in my opinion:
https://www.youtube.com/watch?v=vWax13Inj4g