Do I have a right to be upset at my friend?

I too hate short texts like "ok"and "yea" and "idk". You shouldn't be pissed at him, because if he is purposely ignoring you, it means he is angry at you for some reason. Assuming that you have not done anything to upset him, I'm guessing he is really busy, but you should definitely confront him about this issue, as it if not polite to tell someone you will not be online for a while, without any justification.