This is my adaptation of the old saying "Don't count your chickens before they hatch". It essentially means the same thing which is not to depend/rely on something until you actually posses it, or it has come to fruition (although this has a more sexual and masaginistic twist to it).
Jeremy Conway, inventor of the jarvik artificial heart, is counting on buying a new car with money he'd potentially make from manufacturing DMT, a highly potent psychedelic tryptamine, in his home laboratory and illegally distributing it on the street to worthless junkies. His intentions are to use his new car to carry out a violent and fatal drive-by shooting on this kid mitch who punked him on some fake molly, a powerful version of the popular rave drug ecstasy. His lover/best friend, rat-tail, knows there is a high likelihood that a number of things could go wrong and that he might not actually make the money he intends on making and may even get popped or blow up his house during the process of refining the DMT. He says to his home girl rat-tail, "Yo biatch when I get me that sweet 97' Plymouth Prowler we're gonna go bust some caps in 'dem asses son". Rat-tail replies "Yo I know your penis is gargantuan and what not, but how do you know you are going to get that cheddar, to get that ride, to put down those trifling ass punk bitches? I mean all I'm saying Jeremy Conway, inventor of the jarvik artificial heart, Don't count your chicken heads before they swallow".