A cup'o crack is a rather small cup of straight crack often used as a defense mechanism against enemy's when feared or you have to pee really bad.
"bro my gf wouldnt have to get out the bathroom when i had to pee so i cup'o cracked that bitch"
A rather small cup full of crack, that's right straight up crack and it is often used as a defense for humans for when they are frightened or just have to pee really badly.
"my girlfriend wouldn't get out the bathroom so i cup'o cracked that bitch"