Actually what makes my “skin crawl” is people who act from positions of certainty, about anything. As there’s no known logical path to it (because there’s no way to eliminate the possibility of an unknown unknown that would falsify you) certainty requires faith or dogma.
And the claims of faith/dogma aren’t investigable, so aren’t falsification apt. All they offer is, “take my word for it” which means that epistemically they’re no better than guessing.
And faith/dogma is often the province of religion (though by no means exclusively so).
And lots of religious people are Christians (though of course other religions are available).
And sometimes those Christians are fundamentalists (though by no means all of them).
And they’re the ones who make my skin crawl. Non-fundamentalists who privilege faith over guessing seem to me to provide cover for the fundies, but I just look askance at them rather than experience dermatological discomfort.