A great friend but you want to sound cool or you don't want to say his name. So you just yell that my boi, it also has become popular and many YouTubers have shirts that have that's my boi printed on it.
Guy 1: "That my boi "
Guy 2: "You already know"
"What that guy's name again," thinks guy 1
"His name is so long Iand hard to pronounce and I am never, trying to say it again," thinks guy 2.