During an MSN conversation, something to say after the other participant says something totally irrelevant or something you don't care about at all. For best results, either block the person, or sign out before he/she can respond to it.
From when yoko ono broke up the beatles. People started saying "ono!" When they heard the news, and eventually it evolved into "oh no!". There are no examples of the phrase "oh no!" Prior to this event.
When the parents begin fighting and yelling n shit and eventually they get so outrageously mad that the dad starts brutally hammering their coffee table out of pure rage. This phrase is how the child in the family would commonly respond after seeing the destroyed table.
Wife: I'VE HAD ENOUGH OF YOUR NEGLECT!
Husband: SHUT UP OKAY, JUST SHUT THE FUCK UP!
Wife: YOU KNOW WHAT YOUR PROBLEM IS??? YOU DON'T EVEN CARE ABOUT THIS FAMILY!!!!!!! ALL YOU DO ALL DAY IS SIT AROUND ON YOUR LAZY ASS—
Husband: MOTHERFUCKER!!!!!!!! *inflicts multiple frenzied blows against the fragile coffee table*
Wife: *inaudibly cries in the bedroom*
5 minutes of silence later
7 y/o son: *comes out of the room* oh no... our table... it's broken!