1. Photographic enlarger - I added a switch to control the exposure time but the screws attaching the wires together were also on the outside of the switch that I picked up and pressed with my finger - my thumb touching the screws!
2. Electric fence - out walking on a drizzly day in the country. didn't realise that the wire fences were electrified! Could have been worse - I know people who have urinated, whilst walking in the country, directly onto the wire of an electric fence, not something you do twice!!
3. I was using a keyboard (Roland RD 250s) with a sound module (Roland U110?) and a Jazz chorus amp (also Roland as it happens). When I used the module there was a lot of mains hum. On a gig a "sound engineer" suggested that to get rid of the hum that I disconnected the earth in one of the mains plugs - this worked fine and I was hum free for many gigs. Then one time I had to move location and instead of switching off the mains I pulled out one of the audio cables; the "engineer" had forgotten to mention that the whole setup was being earthed through the audio cables! - got a shock but luckily not of the electric variety and still live to tell the tale.