What is the best way to point out the idiocy of prayer?

Actually, it's not idiotic. Saying prayers is akin to talking over your problems with someone. Praying is theutic. It may seem to be a foolish waste of time, which in terms of results, it is of course. God is supposedly omniscient and omnipotent, he doesn't change his mind, and that invalidates prayer, even if there WERE a god. Presumably he sets out to do something, lets say the death of a relation with cancer. Praying to god is asking him to change his mind and spare the life of that person , and since he is incapable of changing his mind, the prayer is futile. But, the theutic effect of prayer is undeniable.