https://www.google.com/search?q=is+o+a+word&rlz=1CACVLN_enUS931&oq=is+o+a+word&aqs=chrome..69i57j69i60l3.2744j0j7&sourceid=chrome&ie=UTF-8&safe=active&ssui=on it is an informal word (still a word). GOM, I just recommend putting an apostrophe in front of O. Type-ins obviously stay the same.
Example with y: Y do I have to go out
Example with R: R you going out.
Check it in a dictionary