When someone, usually
British or Australian, yells in either
anger, excitement, or fear. It generally needs context, and is usually
said in the beginning of a sentence.
Anger: "Oi mate, you done steal my
boat!"
Excitement: "Oi, look what you've done, mate! Now we can go back to Ireland!"
Fear: "Oi, I think that
big croc is gonna get us."