For taking my 5year old off the bus and leaving her, alone by a busy main road, because the childminder was 5 minutes late.
And then to be furious with the bus company for denying all responsibility (this is a school bus).
The childminder is very responsible but was held up in traffic. My daughter was found wandering down the road by a (luckily) kindly stranger who asked her where I work and managed to track me down.