Have you ever heard the saying the meanest people live longest? I wonder why/where/when/how?

No never heard that one.  I think that would be a misnomer.  What it is is that as we become older we see things change so much around us the world we once took for granted and learned to live in seems to be gone and we miss it so much that in reference to the current world we are perceived as "mean". 

They don't necessarily live longer, it just seems that way to everyone around them. You wish those mean people would just go and die already.

no but ive wondered why it happens that way

I have heard the expression, but my MIL is turning 98 in a few months.  She is a very nice person.

Because we're too ornery to die.