Deliberate mistake: The man kissing Cameron Diaz in that last shot (when the homeless guy shoots the drummer) is not Ben Stiller, noticeable by his much taller, slender figure. (01:52:40)
Deliberate mistake: When Ben Stiller gets done "cleaning the pipes", he looks around the bathroom for "the missing hair gel", he should have known where it was simply by his senses. Earlobes have feeling in them. He should have felt something wet on his earlobe. He also would have felt it dangling from his earlobe.
Answer: Because he is ignorant and doesn't know anything about disabled people, he actually doesn't realise what he is saying is offensive.