This isn't so much of a disappointment as a Santa-disaster one year when I was a youngster - sneeking a peak from the ladder in the attic before the day to check out what pressies had been bought (Subbuteo, Scalectrix, model railway etc) when I dislodged a huge great (and expensive) bottle of "Oil of Olay" that my mum had bought for one of my aunts. Took ages to clean the pink gunk from the carpet (which left a major stain) and explaining the whole thing to my folks was tortuous.
Of course, I can look back on it all now and laugh !