More stories... too much to type on my phone.
In 2000 my grandpa's 81 cb650 was given to me. It was all original, with about 6000 miles on it. The 4-1 pipes rusted out, and i had band-aided it with hose clamps and pop cans. that is just a temporary fix, because the aluminum can eventually blows a hole as well. So, I repaired it with a Mac 4-1 exhaust. I found that the bike didn't run as well afterward. I tried pods, but didn't like getting filter oil on my pants so the original airbox went back in. I replace the stock filter with a K&N. I got a jet kit and installed that as per the instructions. Still, no better. I'd be lucky to do 60 on the highway. Going back through the jet kit troubleshooting guide, it said to wrap duct tape around the airfilter and cover half of it. If it runs better, do this, if it runs worse, do that. No change. I covered 3/4 of the filter with no change. I stopped and thought about it... if restricting airflow doesn't change anything, what if i increased airflow? I pulled the tape off and removed the filter, leaving the cover off. That bike ran like never before! Since then I put the filter back in with some fender washers to hold it in place.
That bike, the cb650, developed a top end leak, so I tore the engine down to re-gasket it. My best friend was there and wanted to scrape the carbon off the pistons. I didn't see the harm in that, so I let him. He decided to take the pistons off the rods to clean them, and in replacing one he dropped a circlip in the bottom. We looked everywhere, turned it upside down, everything and ended up splitting the case to find it. when I reassembled it, I wasn't 100% confident I did it correctly so I took it to a shop. It was about $600 for their guy to reassemble the engine. He said everything was good, except that I put RTV on the mating surfaces between the rods/crank journals.
I had a Buell XB12 for about a decade. I put in a lower final gearset and to do that you need to put a plate between the sprockets to lock them in order to get them loose. I did that, swapped out the sprockets, put the plate in the other way to torque them, and put the cover back on. A few days later, about a week before I was going to leave for North Carolina to ride the roads down there, and the motor locked up. I tried to rock the bike, nothing. I let the bike sit while I rode my Harley down south. When I got back, I found the plate I had used to lock the sprockets inside the cover jammed in the chain and sprockets. Fortunately it didn't seem to hurt anything, but I kicked myself over not taking the time to just pop that cover and look.
Worst thing on my cb750 was swapping to a GL1000 front end. I ran that for several years, put the bike in storage, and when I went to put the bike back on the road I decided to swap back to the stock front end, but I can't find it. I know I had it when I moved, but now it is just gone.
When I was a kid I armor-all'd my bicycle seat once. After that, I'd armor-all the bike seats of other kids and watch them slide off.