One of my favorites is spending nearly 10 minutes trying to get someone to read a single word on their screen correctly, in a dialog box that was blocking them, containing fewer than 10 words, so I could find the cause of their problem. After nearly 30 minutes to figure out that they had a popup blocking them, and not "the computer doesn't work".
What eventually worked was getting them to spell it to me backwards. That strategy has worked out quite well in other cases too - I suspect because it avoids some of people's built-in autocorrect and dyslexia (autoincorrect).
(I honestly mostly enjoy tech support, and I've done it for many years, sometimes professionally. But some people do seem like lost causes, and are not just having a bad day)
The flip side of this is the pleasant surprise of working with a near-retirement age grandma who assures you that she "isn't technical" and "doesn't know how to use a computer", but will studiously write down every keyboard shortcut on little post-it notes and add it to their collection like they're porcelain cats she found at the Sunday markets. I've watched some of these people operate a computer in a manner reminiscent of watching an F1 driver at work, the screen just a blur as their fingers dance over the keyboard.
I have experienced this in person with a developer who was failing to debug something. An error message was popping up on screen and he was reflexively clicking it away faster than anybody could read it. Even after being told “an error message is popping up, don’t dismiss it”, even after being told “[do the thing that triggers the bug] and then completely stop without doing anything else”, and a whole bunch of other ways of phrasing it, he was unable to understand that the error message contained useful information that we needed to see. I’m not even sure he was consciously aware it existed or that he was doing it. After many failed attempts at getting him to stop I literally had to take the mouse away from him and do it myself. I was shocked that apparently nothing anybody could say would stop him from dismissing the error message without even looking at it.