An interesting read here: http://www.quickanddirtytips.com/education/grammar/on-accident-versus-by-accident

I'm 28 and I say "by accident" and always have.

But I also tend to avoid kids. Its usage was however brought up not long ago on the radio show/podcast "A Way With Words".

It was definitely seen as a "generational shift"... It still sounds simply wrong to me.

Learning which ones are "right" in a foreign language is a pain in the ass.

"On accident" actually sounds more reasonable to me.

He slipped on the ice. / He slipped by the ice.

"On" is more closely connected to the slipping than "by."

"On" is more closely connected to the accident than "by."

Language evolves.

"By" is probably acquiring a more literal meaning than it previously had, closer to "nearby" or "next to."

For what it's worth, I don't pay attention to people who question my spelling or grammar and I never have unless it's some error that entirely confuses my intended meaning.

Inside my head I've got a writing mode and an editing mode. If I engage both at the same time then I'm unable to write at all. The gears lock up. If I want to post something here on DU, I post it here now, rather than editing it and posting it later.

All those awkward phrases, comma splices, and huge messes of other bad grammar are simply my writing raw.

Kids.

Whaddaya gonna do, right?

it is the opposite of "on purpose" and easier to mentally default to the opposite of an already existing phrase than to actually try & remember the correct phrase.

or

perhaps part of the initial usage of "on accident" came about as a "cool" new rephrased sort of way to say "by accident" -- if you were hip you spoke hipster. but over time the phrase remained but the rationale behind it was lost. now the people who use it are unaware that they sound like idiots whereas, initially, those who used it intended to sound like idiots *on purpose!!*

(am i over thinking this?)

"no, wait! i lied."

you LIED???

lying implies whatever was said was intentional. but this "i lied" crap is used in place of: "i was wrong," "i meant to say," "i made a mistake."

my adult daughter CONTINUES to use this expression that came about either in jr. high or high school. i have never been able to break her of this habit.

All the kids around town say "We versed them last week" when talking about a ballgame, or something.
Makes me CRAZY!

To top it off, our school's athletic boosters use "verses" on Twitter ("Come see our home team verses the Bears" or some such).
I'd reply with a snide "versus" every time they do that, except they'd know it was me.

And you kids get off my lawn.

"On accident" or "by accident" implies an action.

I don't like it.

I've heard it on and off for years.

(Also, people here say, "I carried him to the store." What? I couldn't carry anyone very far at all. But they mean something like, "I drove him to the store.&quot

Back in New York, it was "by accident"; here in the mid-west, people say "on accident" just as often.

Also, with people moving around the country, these linguistic differences spread.

I've always said 'waiting in line' but now it seems more common to hear 'waiting on line'. When did that change? And when they start using the word 'queue' instead of 'line', I'll say "well, lah-dee-dah" and throw in the towel.

Or maybe it's because we're indoctrinated into computer lingo, i.e., "print queue."