Suppose you are in your late 70s. Suppose further that your teenager grandson is explaining to you some features of a smartphone. "Do this, do this and Bob is your uncle!" Would you take umbrage at the use of the phrase?
It's alive and kicking in Australia. Young and old know the expression and use it. Sometimes you'll even hear a child use it (they've heard it and will repeat it - as children do - because they think it's amusing).
Is it ever said as "Bob is your uncle" as in the title, or is it always "Bob's your uncle"? I've only seen "Bob's".
This expression isn't used in AE, but I understand it. The first time I heard it, I probably felt like the dwarf in a Terry Pratchett novel, who hears a human say "and Bob's your uncle!" and replies "But, surely Thor Stronginthearm is my uncle?"