If I could get in-depth without sounding academic.....
The more into language you are, the more slang you use, the larger your vocab, etc........the more about Borat you'll "get".
For example: Saying "make a sex" or "sexy time" is 100x funnier than just saying "fuck", especially when a foreigner says it. When he says shit that no English speaker would ever say, like "sexy intercourse".....me personally, I'm ready to fall out of my seat. -- It's not just the accent or saying things in a funny way.....he CREATES new shit.
Sure, there's the Racism and Sexism, and making people look stupid, but me personally, it's the Borat Vocabulary that kills me.
Oh yeah....movie i didn't find very funny...... Old School. Anchorman is one of my all-time favorites, but O.S. just wan't it.