It's common sense that you shouldn't stare directly at the sun, especially through a telescope, but any time there's a demonstration that backs up common sense, I'm onboard.
Mark Thompson recently posted a video on YouTube demonstrating what happens to a pig's eye when it's placed under a backyard 80mm telescope with 50x magnification facing the sun. The video may not be for the squeamish.
The video was posted because of the upcoming Mercury transit coming up May 9. You can read about it, and how to safely view it here.
Just because it's common sense doesn't mean we shouldn't continue to spread the message: Don't look directly at the sun!