Rube isn't a word used in Britain. As far as I know it's not used in India, Australia, South Africa or New Zealand. either.
This, I believe, is something to be celebrated.
My Collins dictionary says that a rube is 'an unsophisticated countryman', and of course there's nothing wrong with being unsophisticated or a countryman. But look a little further and rube begins to look nastier: according to Wiktionary a rube is not just a yokel, but an unintelligent and uninformed yokel.
In spite of this, rube is apparently used by respectable people. Here, for instance, are the words of a famous sophisticate (director of the Baltimore Philharmonic Orchestra, no less).
'You look like a rube...you're not more than one generation from poor white trash, are you Agent Starling?'
So if you're filled with an urgent desire to emulate Hannibal Lecter...
...hmm...perhaps there are worse crimes than using the word rube, after all.
But I'd strongly advise abandoning anyone who does.
Sunday Rest: rube. This 1900s word is short for Ruben. In Hebrew it means Behold, a Son!