A polymath is someone who knows all sorts of shit about all sorts of shit.
You don't need an encyclopedia, you just need your own personal polymath.
You know that person who constantly interrupts you while you are speaking to interject their commentary because the feel that the situation somehow has something to do with them? That person is rude. They are also probably not a polymath, though they could just be a rude polymath. A perfect example of such a person would be Tyra Banks. On the other hand, Ken Jennings, the guy who won Jeopardy for 74 weeks in a row, he is probably worthy of the title.