Roger, here is one to kick off. Some might not find it funny but for some reason it always makes me smile when I think of it.
In the 70s I came across my old man in the dining room, fiddling with an unusual contraption; I asked him what it was and he said its a sun lamp, your granny loaned it to me to see if it will help with my sore knee. This thing was out of the ark (no pun intended, but appropriate as you will realise), it was a circular dished reflector, with two carbon electrodes across the front of the reflector with a bakelite knob at each end of the electrode. The idea was that you turned the knob inwards until the electrodes touched and then you slowly wound them apart thus creating the arc. So, visualise this, he is crouched down in front this thing, winds in the electrodes then proceeds to wind them out, but as he does so one of the knobs comes off in his hand leaving this carbon rod exposed. Before I could say dont touch it he grabs the carbon and is instantly thrown across the room, jumps up cursing and swearing like I never heard him before.
I never laughed so hard, a combination of relief he was ok and the reaction to his "electrified" response.
He never complained about his knee after that, but a week or two later did his nut when my granny innocently enquired if it had helped (triggering another bout of uncontrollable laughing by me).