I'd fitted a new electric shower, really happy with my efforts. Put new fuse box in (going back about 15yrs, so no Part P) in the cellar, cabled up thru' the kitchen, into the bathroom and into the loft so I could install the pull switch then into the shower unit itself. Switch it all on and it worked first time 8-) .
I then used it for real and just as I was fininshing the whole unit switched off. Got dried and checked the fuse box in the cellar - all OK. This happened a couple of times which was getting annoying. The final time I was mid lather (must have taken longer in the shower this time
) so I quickly got some clothes on and ran into the cellar, screwdriver in hand to take everything apart and re-do. It turned out that it was the earth strap that I'd put on the cold water pipe (copper) and I hadn't tightened the screw up so that when the water flowed (to supply the shower) condensation formed on the pipe and broke the earth connection. Mildly amusing to me. Looking back tho' I was still soaking when I was playing around with the mains electric 
I think I was lucky considering a story I heard a couple of days ago about a boy who got electricuted playing with his GameBoy with it connected to the mains having just got out of the pool without drying himself 