No, I do not think that would be a good idea. There is no point in highlighting "bad" opinions. All that would do is cause drama. If you see an opinion that you disagree with, that's what the down vote button is for. This is supposed to be a positive site. Giving out Most Helpful's shows appreciation to user's, selecting a "most poisonous" opinion is doing nothing except humiliating a user, which I do not agree with. I don't see anything good or positive coming from something like that.