More memories so here I go again. Our instructors were generally held in high regard and we wouldn't have dreamed of doing something like that to them. I have to say though that hours and hours, nay weeks, of hacksawing and hand filing test pieces in the hand fitting classes were pretty tedious but I later much appreciated the skill and "feel" it gave me when seeing the absolute hashups some, supposedly skilled, people made of things. One of our favourite "tricks" was to put a large metal funnel - we all made one in the "tin bashing" classes (I still have mine somewhere) - spout up on a flat bench and trickle coal gas from the shop blow torches (which were there for brazing exercises) inside. Then you would light the gas from the end of the spout which would burn like a big candle as it pulled in the surrounding air. Of course as this burned it sucked air into the bottom, large diameter end, of the funnel until enough air had mixed with the gas inside whereupon the flame at the end of the spout, because there was now oxygen inside the funnel, would ignite the mixed gas inside and the whole funnel would take off as the gasses inside exploded! A "good one" would reach the roof!
Another "silly" one involving HT was when you got into the engine shop - one of the most interesting modules I did at the college - where there were live engines, one on a water brake for recording power runs and others for fault finding and tuning procedures etc. One of these was a VW flat 4 from a Beetle. The "trick" was to pull one of the HT leads when the engine was running and hold it behind your back. Then as another unsuspecting student approached you would say "Hold on a minute, just look at you" and extend your other hand with forefinger pointed at the unsuspecting victim's nose. When your finger was almost touching their nose there would be a loud snapping noise as the spark jumped from your finger to his nose. The results could be very funny but could also result in perpetrator ending up with a black eye or broken nose from the punch delivered by the victim of the prank. I never did it because I couldn't hold onto the HT lead without jumping around too much and giving the game away!
And a last one, regarding Health and Safety, which back in those days was almost non existent. Our workshop was heated by a waste oil burner which, if I remember correctly, was called a Volcano. This fiendishly dangerous device had a large round tank at it's base - maybe 3 feet or so in diameter? - which the old waste oil was emptied into together with a gallon or so of paraffin to make it burn better. On top of that was a funnel chimney which flared out a bit until it got near the top where it then turned back in again. It looked a bit like the smokestack on one of those old wild west steam trains. The side of this chimney was punctuated with many louvered holes. It worked by filling the base about two thirds full then throwing a lighted rag on top of the waste oil/paraffin and putting the funnel in place on top. At first there would just be a gentle flame going up the chimney but after a while the oil would get so hot it started to vaporize and then it really got going. The whole chimney would glow red hot and it mace a pulsing roaring noise a wee bit like a rather quiet ram jet. It gave out prodigious quantities of heat, you couldn't get within a yard or so of it when it was on full song, and made the back of the workshop a nice warm place to be. Often in the winter when the main workshop doors were open, we would all spend time standing around it to warm up again. The most serious incident involving it was when our apprentice (we only usually had one or two apprentices) had been cleaning down a couple of engines and gearboxes using our high pressure paraffin gun. This gun produced a lot of paraffin vapour which was inevitably absorbed into your overalls. This lad was standing with his back to the Volcano at tea break and wee were all sitting around on the old sofa and car seats which we used to relax on during breaks. I remember looking at this young lad and seeing a light cloud of what I took to be steam coming off his overalls. As he'd also have been doing car cleaning I didn't give it a second thought until the foreman leapt at him in a rugby tackle type move and knocked him away from the fire. The "steam" wasn't steam at all, it was vapourized paraffin! The poor lad had been just moments away from going up in a ball of flame! We were all gathered around by the boss with the foreman standing at his side and given a "serious" talk about workshop safety and how we were not to be so "silly" around the Volcano. The fire continued to remain in service though! Later that day I complained about a trolley jack which, in all the ime I'd been there, had never had a saddle. I was told "Oh yes, I know about that, I've got one on order" Don't remember it ever being replaced though.
No wonder Health and Safety became such a big deal. By the time it became important with risk assessments etc I was in workshop supervisor/manager type jobs and I remember thinking "this is all very well but it's going to cost me money and lost production time" Then in later years, as an instructor, I actually flipped 180 degrees and found myself doing risk assessments almost every day of my working life and being 100% committed to the concept.