I must say this first: I don't like watching dubs, not only because a lot of the original content is lost in translation (which can't be avoided for those who don't speak the original language), but also because you can't hear what the characters were intended to sound like, and the acting in general doesn't sound very natural. I prefer to hear the voices of the actors who played/voiced those characters originally; even in the cases where I can't understand most of the words, there's a lot of expressiveness in the voices and the intonation which is lost in dubs.

That said, some dubs made by good actors can manage to be somewhat decent, and I would recommend them for little children who can't read fast enough.

Some dubs try to make up for the jokes which are lost in translation by replacing them with more or less similar jokes in the target language which should make sense for the intended audience. I've very rarely seen this approach actually work.

And then... some dubs are really, really awful. Such is the case, for example, of the Mexican Pokemon dub (at least up until 2005, I haven't bothered to watch the rest). That dub was so terrible that every episode was full of inside jokes and references that only people who knew a lot about Mexico could understand. And of course, I didn't get most of them. But I did learn some Mexican slang and some facts about the agricultural production of Zacatlán from watching it.

Now there was one reference that had been bugging me for years, ever since the Pokemon horoscope episode. James was claiming to be a Moltres and called himself something I just couldn't understand: Guajolotón Macías. Later, I learned that the first word was derived from "guajolote", which is Mexican slang for turkey (okay? What does a Moltres have to do with a turkey other than being a bird?), but the 2nd word was still a mystery. Until today. Today I was browsing Bulbapedia and I learned that Macías was the last name of the voice actor who voiced James in the dub. He called himself by his own real name! Why did he do that? How was the audience supposed to get it?

So there goes my rant about the worst dub I've ever heard. What about the rest of you? have you heard any dubs with inside jokes or things that you just didn't get?