A scrawny white guy with penis size issues is using a urinal trough at a bar one night when a large black man steps up beside him unzips his fly and releases a monster to start taking a leak.
The white guy glances across and catches sight of his neighbours huge member and scoffs in disbelief "I don't farking believe it, why do you black guys have such massive cocks!!??"
"I was born with a little dick and I've tried everything to try and get it a bit bigger, all the pills, all the machines and nothing works, how come you guys just get born with these huge dicks?"
The black guy, seeing an opportunity to have some fun and mess with the white guys mind says, "We're not born this way brother, we have to work at increasing the size of these things, but it is a a bit of a cultural secret and I shouldn't really be saying anything about it".
Amazed by this comment the white guy, begs for more information on how to make his old fella as big as a black mans. Eventually the black man says, "Man, you need to use gravity! Gravity is the key. Tie a piece of string to a brick, and then tie this to the end of your penis, adjust the string length so that it just hangs the brick mid air over the side of your bed when you are sleeping, do this each night and gravity will do the rest"
The white guy thanks his new best friend and rushes home early to trial his new technique.
Several weeks later in the same bar, the black man bumps into the white guy with penis issues once more. Expecting to be punched for giving this desperate man such dodgy advice, he sheepishly asks whether he has continued with the gravity treatment and if he has noticed any progress.
Much to his amazement the white guys enthusiastically confirms that he is indeed continuining with the gravity treatment and in regards to progress notes that "I'm half way there".
Curiosity gets the better of the black prankster and he asks,"What do you mean half way?"
Proud as punch, the white guy says "It's Black!!!"