I keep forgetting to come back here and start this thread. I have a few mondegreens that float around in my brain and every now and then pass by the viewing window like underpants in a front-loading washer, but for now I'll just drop in the original.
The American writer Sylvia Wright coined the term in 1954, recalling a childhood memory of her mother reading the Scottish ballad "The Bonnie Earl o' Moray", and mishearing the words "laid him on the green" as "Lady Mondegreen".