“Sorry, I didn’t mean to bump into you. I did it on accident.”
That’s language I would use. I had no idea it was nonstandard. I’m in Michigan.
Same in California. Nobody but English teachers complain about it.
I’m in west Tennessee and that is my experience as well.
It’s looking like this may be a mid-southern expression.
Fascinating. I grew up in SoCal but left in the early 1980s and have not lived nearby since. I totally do not recognize “on accident” from there then. If anyone ever said it back then, they sounded like a total Okie hick doing so.
A few years ago I met someone who regularly says “on tomorrow” (I may have even made a post about it). It appears to be a Southern thing
I hear "on accident " fairly often, but always with a bit of a tone indicating thst the speaker is being deliberately (mildly) funny
I grew up here and still live here. I’ve started to hear “on accident” over the last decade or so, but it’s kinda like fingernails on a blackboard to me. I don’t say anything or object to it. I just find it clunky and dumb sounding.
I’ve never heard “on tomorrow.”
Hmm. I’m also from Arkansas, but in the northern part of the state. I’ve not heard “on tomorrow” or “on yesterday” either. I would omit the “on.”
Come to think of it, though, I can also omit the “on” with specific days of the week. “I’ll have this ready for you Tuesday” means the same thing as “I’ll have this ready for you on Tuesday.” But, in those cases, both sound fine to me.
I’m also curious: are there any situations where they do not use “on”?
Never ever heard that before. (On tomorrow.)
I can’t say I’ve done a great job keeping track well enough to notice. It took me a while to even think I should ask if anyone else ever hears someone say “on tomorrow.”
Given the ongoing level of immigration to CA from the midwest and northeast, all sorts of ignorant impure speech will soon be ruining has already ruined the pure dulcet tones and wisely ideal idioms of traditional SoCal English. 
I think you’re right! 
It’s preferable to believe that “on tomorrow” never happened, like “sweet tea”.
I haven’t heard it but it sounds vaguely like constructs used in countries where English is very popular but still a second language. I have heard people from India say things like, “today morning” and “do the needful” that I don’t hear from other English speakers.
I understand your meaning about “youngling”, but note that “Youngling” has been in continuous use in English since before the Saxons came to Britain.
Wow. I did not know that. The one and only place I’ve ever heard it was in that film.