As a much younger Toyota Tech I was asked to take on an apprentice by the shop mgr. The apprentice spoke almost no English, he was an immigrant from So. Korea, a former ROK who was in an accelerated-citizenship program in return for his having served our side in Viet Nam on special missions. (This guy was very polite, but I wouldn't want to be on his bad side. He knew how to kill in more ways than the average soldier.)
Anyway, the shop mgr had 10K miles on his own Toyota pickup and wanted a "ring job" done under warranty. (Stupid idea that somehow taking a properly broken-in engine apart and installing new rings and bearings would benefit his truck.)
Anyway, the mgr wanted my apprentice to gain some heavy engine experience so the ROK was to take it apart … "but I want YOU George, to put it back together while showing him how!"
I was off at recurrent rear axle training while ROK took it apart, but I'd given him careful instructions on how to lay out and identify the parts during disassembly. When I returned two days later I reassembled the engine in front of him explaining what I was doing (and having zero confidence he understood any of it... I think the most complicated machinery he'd ever operated was a .50 BMG.)
I decided that when it came to adjusting the valve lash (in 1972 Toyota still had mechanical Ovhd valves) I'd let him do it under my watchful eye.
I handed him my expensive Snap-On 14" long set of individual feeler gauges … and mindlessly watched him lay them down.... across the battery terminals. They went incandescent instantly and before I could think I grabbed them with my bare hands. Ouch.
Next day, with bandaged right hand, we tried to start that truck and it refused to turn-over at all!
ROK had marked the main bearing caps as instructed before I went off to training. He'd removed them, turned around and laid them on the bench, and marked the end of the cap with an elect. engraving pencil... but failed to recognize that by turning around to face the work bench that the end of the cap would now be mirror-imaged... so they were marked exactly backwards!
Because I'd agreed to take on this apprentice... I was the one who had to pay for the complete new engine for the shop mgr's truck even tho' it was the shop mgr who wanted the unnecessary engine work done by the untrained foreigner performed while I was sent off to school by that same shop mgr.
Besides the docked pay-check I had the burned hand and ruined feeler gauges. The next week, ROK started a manual transmission Corolla by reaching thru the drivers window....while it was in-gear … and the only reason it didn't take out the shop-wall... was because my new roller tool-box was between the Corolla and the wall.
I still have that dented roller box in my shop, bearing the scars and dents from that 1972 apprentice. I took the roller box with me when I changed Toyota dealerships to get away from that shop. Dumbest thing I did....? was to not make the shop pay me for the engine work, the medical costs of a burned hand, and a damaged roller box.
Oh yeah,... I did get a little revenge however. When he was overheard bragging about how he could karate' chop bricks in Korea.... I got my revenge by not telling that ROK it wasn't a good idea to demonstrate his karate' chop on the American-ACME kiln-fired bricks the other mechanics set out for him in a beer-bet.