From the movie Serenity (2005)

bibbledy = crazy?
Can you find any dictionary definition? Is it some kind of informal silly slang? Is it rare?

It’s a made up word specifically for the movie.

In the Official Visual Companion to Serenity, Joss Whedon describes the language of the verse as “basically based on everything”, but with “a healthy dollop of made-up Joss talk”. … w.php/2253

I’d say your guess at crazy (in the sense of being overly enthusiastic and excited) is correct.

Actually it must be crazy in the sense of having lost one’s mind cause the people the speaker describes are the Reavers who are “exceedingly aggressive and violent” as well as “savage and cannibalistic”. Later on the plot it is revealed that this dramatic change in behaviour had been due to a chemical experiment and not some kind of travelling experience.

But thank you for your time.