When I'm faced with some moron who thinks he knows everything there is to know about everything I respond in one of three ways:

1) Ignore him. Because opinion are like armpits--they all stink.

2) Tell said moron "Those who think they eveything are annoying as h*%l to those of us who do".

3) Remember Murphy's Law about arguing with idiots.

As has been said before, real friends will accept you as you are. Family is lot tougher.