While I somehow never get emails from cranks, I tend to find them at the slightest provocation on the internet. Here’s a new one: Miles Mathis, who I’ve not run into before. He’s also a physics crank (multidisciplinary research!) so for the more mathematically minded, just jump down to Section 2, where he has some deep-seated problems with calculus (implicit differentiation seems to have caused him to label the Calculus as corrupt), and there are some other gems mixed throughout. For instance, the page I found, on non-Euclidean geometry.
On a more productive note, I was searching the internet for things I can bring up in the class I’m teaching to point out the flaws in Euclid’s framework, that were due to him relying too much on certain bits of intuition (between, inside, continuity, etc) without spelling them out. If you’ve got a good example, please link to it in a comment.