what a great thread, good to know everybody cocks up from time to time!
I've called little owls several times that turned out to be things like the ceramic mount on top of electric fence posts; once I briefly mistook a small black rabbit for a blackbird (it was amongst a flock of sparrows and starlings for some reason); I even somehow mistook a skylark for a turnstone (it was on a beach flipping through seaweed, but still....).
I work with kiwi so some of the best stories are reserved for non-birders -- I know its not right to mock people who don't have any real interest in birds, but I'll do it anyway

Most of the "kiwi" I have been told about are weka which is understandable but the tourists do wonder why kiwi are considered rare when they had dozens of them stealing their spoons when they were camping. Two American girls said they'd seen kiwi on the banks of the Avon in Christchurch (the best I could suggest was thrushes or female blackbirds -- they were sure they weren't ducks!). Its very common for tourists to see kiwi "all over the roads" while they're driving. Best of the best is the Nigerian guy coming to NZ to study who caught a kiwi in his garden on his first night in the country. He put it in a box and took it to his school, and was told "um, that's a hedgehog..."
(And on that subject there was a kiwi caught in Melbourne in the 80s or 90s that was taken to a wildlife rescue centre where it turned into a juvenile night heron)