You're at a party, and for some reason are arguing about the nature of religion.

After a few minutes of stereotypical debate, the religionist claims that

You just have to take it on faith.

You respond with

Well, faith is a fairly modern invention. Originally, people thought that their beliefs actually had to correspond with things that they observed in reality. People would convert because their God would lose to someone else's God in some observable field, or because their rituals were less effective. The way you're using 'faith' is mostly based on some mistranslated Greek words, and only seems to have appeared in response to religion being shown so wrong across the board that the only possible defense is to deny thinking itself.

Now, the religionist is probably going to be pissed off at you, and isn't going to change their beliefs. But every agnostic around will entirely lose respect for the "Faith" argument, and maybe turn outright atheist.

It also would defuse statements like "Humans are wired to have faith."