derogatory noun reffering to people from the inland empire, used especially in Newport Beach. This is a shortened synonymn for 909er. Possible ways to distinguish a nine-o are trucker hats, older lifted trucks with gigantic volcom stone or famous star stickers, wife-beaters, a smoggy residue on the clothing,and a complete lack of mental aptitude and class.
I cant believe he is wearing a trucker hat and a wife-beater. What a nine-o.