I'm surprised that a number of forumites are familiar with the word pepito, because I can't see it in any dictionary, except Wiktionary, which lists it as an obsolete word for a gold nugget.
And my searches didn't show much use of the word in English language publications. Searching isn't so easy, since Pepito is a proper name. The Wikipedia article that ridethetalk quoted does have references, but at least one of the books referenced prints the word in italics, suggesting that the authors or editors didn't regard it as a fully naturalised English word.
I'm not convinced pepito is well enough established as an English word to warrant inclusion in Chihuahua.