Quit showing your cards when you fold in a multi-way pot!

[BigFishSmallCardRoom]

I would call the floor over every time it happens until people stop. If that doesn't do the trick, start folding every hand face up preflop until the table is in an uproar. People only get the point when it affects them personally, so start messing with their odds and screw up the hand, especially when you aren't in the hand.