people respect it when you set them straight
take him aside where no one can hear
and talk to him man to man
make it a point to be heard
he most likely wont agree with you
and you two may end up squabbling a lil
but in the long run he will respect you and may even listen

JUST BE SURE AND KNOW WHAT IT IS YOU ARE TALKING ABOUT
GET SOME GOOD OLD CONCRETE FACTS THAT BACK UP WHAT YOU SAY