used in London by youts who are espeically into UK garage and Grime. When someone implys that another person is a boi, he/she is saying that the victim is a pussy or in other words a "shook up bitch"
boy 1 - "who's dat boi!?"
boy 2 - "oh yeah! he's the one that got beat up by some 9 year old"
boy 1 - "hahah wat a BOI!"
When you are roasting someone because they are simply and idiot, and you want them to know it. It involves a hand movement that you have to make a straight hand and point it to the idiot, having the thumb and pinky verticle.
IDOIT- Heh, she said but... like BUTT ! hahahahaha
BOI-ER- Boi, are u like 5?