@Zee...first of all, your post to @Catrice is full of grammatical errors. I would not be quite so judgmental if the entire post wasn't about how well you use the English language.
Now that we have that out of the way, I would like to address the issue at hand. "On tomorrow" is unfortunately used at the school where I teach. The administrator that uses this phrase, along with "on today", "on yesterday", etc., is indeed a black woman. Nothing racist about that FACT. Just because you are an exception to the black population, doesn't mean that our observations are not true. "It is what it is"(for lack of a better/more grammatically correct phrase). I have also heard her husband use the "on tomorrow" phrase, and he, too, is black. Racist? No, I think not, but people such as yourself seem to always be on guard-ready to defend the entire black population simply bc of the color of their skin. There are poor examples of people in every race and culture, but that doesn't mean that you and I are represented by those bad examples.

Also, one last note : The topic referring to the "soda water" vs "pop" does not belong on this thread at all. These are true examples of cultural terminology; the difference being that any of the terms for a fizzy drink are mere preferences according to the region from where the speaker originates and is not "slang" nor grammatically incorrect phrases as opposed to the controversial "on tomorrow" faux pas.

I must say..I came upon this post because I, ,too,have heard it more than a person should have to endure!!! Sadly, I am a teacher, and my administrator uses it every day-yes, this phrase is broadcasted for all the students!!!! It drives me nuts, and we teachers snicker behind his/ her back-but none of us would DARE correct him/her. I've not done any research in the matter, & I do not claim to be an expert, but, I do have a couple of undergraduate degrees in education and a Master's degree with an add-on specialist certificate in Reading Education. With that said, I live in the South-Georgia, to be exact, and I was educated in the very system in which I teach-a public school system where I was never, EVER taught the phrase "on tomorrow".

Oh yeah, did I mention that my admin is African-American??????
"Just sayin"