How about teaching a guy twenty years older than me how to send a fax? Not really a horror story, but more of "how do you not know this?" frustration. Showing pretty much everyone keyboard shortcuts to do stuff, really simple stuff. Ctrl+v simple. I think a lot of people hate computers because they never learned how to make their lives easier with them. As soon as I got my first dot matrix I put the typewriter in the closet and never looked back.
Everyone who owns an iPhone seems to have problems with them, but they come ask the guy who hasn't bought an apple product since the video ipod came out. When you tell them to Google it, they get mad. When I was in the corporate sphere, a lot of businesses would give you a phone, so they have people on payroll to ask these questions. Got so much worse with forced diversity, that by helping these people, you enabled them to keep being shitty. If you show someone how to do it, they will never learn, if they have to learn to survive, they will prosper.
When we graduated high school my friend started going for an engineering degree, and before he even graduated, he was already promoted off of the job site. He was 20 years old making more money than guys in their 40s, because he used his free time on the job to read the equipment manuals and took the free class the company offered to get a certificate that allowed him to operate that specialized piece of equipment. This was something offered to everyone, but people were fine with just digging ditches so to speak.
I hope you got a pay raise as a designated instructor. You can learn at any age, people just choose not to.