it's a word from my childhood, used to mock someone who'd done something wrong by accident.
1. collect the eggs, trip over your own feet and break the lot, bringing mocking and laughing and shouts of "dunderhead" from siblings and/or dad.
2. prepare a mug of hot chocolate mix and instead of the kettle of piping hot water, absent-mindedly pick up the teapot with cold left over tea and fill your mug. "dunderhead". And if mum was in a bad mood, she'd make you drink it.
and so on.
I heard it often up until I was maybe 15 or so, then it fell out of fashion I suppose, I haven't heard it since and have no idea why it popped into my head today.
It's one of those words that was only directed at boys for some reason, girls were never called dunderheads.
They must have got called something, but I don't recall what that was.
Do you remember any odd words from your childhood?