(comes from the meaning of to bust a nut ...
if you are jerking off and you come/cum
really fast then your nut just might explode)
person A: "Man, you really busted a nut!"
person B: "Yeah, I just cranked out that whole paragraph in 5 minutes."
Originated from busting semen out of your testicals(nut) which is where your semen is stored. Thats why they call it busting a nut. Busting semen out of your nuts.