While there are plenty in the field of xenophobia that make me lose hope in the compassion of people, intelligence wise is when someone tells me that they (or someone else we know) doesn't believe in dinosaurs. We have so many fossils that the proof of dinosaurs is undeniable....or so we expect from someone with brain-cells. I know it stems from religious fundamentalism, but imagine if someone said Julius Caesar didn't exist? They'd be thought to be crazy or just plain stupid.
What makes you just shake your head at people?