Thats my personal favourite, when you turn at the house and the husband is hiding upstairs and the wife tells you "my husband changed the light fitting and it was working" i always think man up and face me !Exactly the same, hate house bashing and charge double what it would have originally cost to change a pendant to a light fitting when they connect all the blacks and reds together and wonder why it goes bang (now brown and blue, god I hate the new colours!). Everyone thinks its easy till it goes wrong or up in flames.
The bit that gets me, you would think when taking the old light down they would look at the cables and see that all the reds/browns and all the blacks/blues were not connected together.
Im a pretty experienced sparks but if im taking something apart that has multiple cables/colours connected or something out of the norm i always get the phone out and take a snap, saved my arse many a time when putting it back together several days/weeks later !