It has to be American, of course; nobody but an American would use a phrase like herpdty derpty, so I’m hoping that somebody from the star spangled sub-continent will enlighten me. It sounds like the sort of expression that would most likely be used by a young woman, but how can I know?
This is earnestly meant. I’m only just coming to realise that a lot of those quirky Americanisms are not only fun but also keenly expressive, and I do think we speakers of the Queen’s English might adopt a few to our benefit – by way of starch reduction, if you see what I mean. So no hailstones, please.