Seconded. I've never heard this in the UK from people of any age.
I wonder if it has anything to do with the way "an" sounds when spoken with an American accent. A mishearing and then repetition of "an accident" seems much more plausible to me than confusion with "on purpose".
"An" in American sounds like "Anne", so I don't think that explains it. As an aside I've never heard someone say "on accident" so it might just be stupid people. Another good example is "would of" instead of "would have".
No, but we have a similar one - lend and borrow have become interchangeable. "Can you borrow me an X" or "I lended (not even word AFAIK) it from him" is one I hear often from younger folks.
That one I understand. It was an exception anyway; lended is more straightforward. Like 'builded' vs 'built'. The sign on our old 1800-era edifice says "Builded 1838" so I guess they used to use that (or at least write it that way)
I wouldn't usually just throw out a data point but since so many people here are saying they haven't heard it in the UK, I'm in the UK and certainly do hear "on accident" occasionally and have used it myself - it is less common though (An exclamation of "it was on accident!" is the most natural use I can think of - which fits with the idea it came via "on purpose"). Disclaimer: I am somewhat into youth culture and use a lot of slang in everyday speech.
(So I just asked my employees - who are somewhat younger than me. They had heard of it, claimed not to use it, and believed it was poorly educated people with a poor grasp of English who used it in their experience.)
Funnily, "Me either" is also an americanism that seems rather foreign to me. (Me neither would be more likely to be used in the UK in my experience). I think both are rather informal and so neither is necessarily incorrect.
I've never heard 'on accident' out of a British person, even living in Canada. I've heard it out of many Canadians and Americans alike - but I've equally heard many of them use 'by accident'. I hadn't registered the generational divide though. I thought it was just commonly used in both forms [even though I personally correct them in my head every time they do it]. It grates on me when they use "I could care less".
What also bothers me that I've heard out of many British people, but never yet a Canadian or American is 'can I lend that thing from you?'... you can't lend something from its owner. As the lender, you are the owner of the property to be lent. Thus you can lend something to someone or borrow it from them, but you can't borrow it to someone or lend it from someone.
I wonder if it has anything to do with the way "an" sounds when spoken with an American accent. A mishearing and then repetition of "an accident" seems much more plausible to me than confusion with "on purpose".