First of all, fansubbers tend to embellish a lot.
Japanese doesn't have a lot of swear words. There is no real equivalent to "fuck" in Japanese, unless you say "fakku" or "fukku" or something, so in subs when you see the word "fuck," it's only the translator throwing it in there. In official subs like the ones on DVDs, there's not as much swearing.
Here, look at all these fansubs:
I don't really know the legitimacy of these subs, but they're pretty damn funny when you come across them. xD I also love it when subbers comment in the anime, especially at the beginning of episodes when the sponsors are being shown.
When I was watching the Naruto fillers, the only thing I could look forward to other than finishing them was the little notes at the beginning of episodes. Even if they weren't all that funny, I couldn't stop myself from laughing. Usually they said stupid things like: "I hate these goddamn fillers," but with Naruto they would actually reference the episodes. I remember one episode where Zetsu showed up on screen, and the note at the beginning read: "Zetsu da." meaning "That's Zetsu." and the next episode the opening note was "Zetsu deshita." or "That was Zetsu."
Somehow, even stupid phrases like that were really funny.
It was probably because the font used in subs feel so official that when the subbers write in jokes or little notes, you can't help but feel as if the characters of said series are associated with it. GOD, it's really hard to explain, so just fucking laugh, okay? I don't want to explain the logistics behind why I find things funny because my sense of humor is really fucking messed up. :/
It's also funny to see fansubbers make mistakes. We all make mistakes; it's just funnier when the super cool fansubbers do it. xD
I've never seen Mishi-Corp subs, but for some reason I feel as if I should give them a try now. If only for the lulz.