The most endearing of terms for your friends even when they are completely mentally retarded
Friend: dude did u see that post!?
Me: boi
boi is a word is where you acknowledge someone's stupidity (either in verbally or physically) and point it out to the person being an idiot. You point it out by putting your hands together and pointing at them (optional).
*Tries to jump over car, but fails epically*
man sees and says, "boi"
A fuck boy. Friend with benefits. Boyfriend material without the commitment or title.
That's my Boi toy. - referring to fuck boy