Inverted with 23 year old Seth Rogen as Cal who is implied to be much older.
Dyeing for Your Art: The chest-waxing scene? Yeah, one hundred percent real. Ouch. For the obvious reason, this was a one-take scene. In fact, at one point they almost ripped off Steve Carell's nipple, because they forgot the stuff that you're supposed to put on nipples to prevent them from being ripped off. You can also see his blood starting to bubble out, as noted in the commentary.
Throw It In: All of Andy's exclamations during the waxing scene were improvised by Steve Carell out of the real pain he was going through. Apatow kept separate lists for profane and non-profane ones, so they could mix and match as they pleased.