When a male has not masturbated/had sexual intercourse/any in the pants action for a long time he will get lots of semen building up in his penis (also known as cock). So when he next pleasures himself he will produce a larger spurt of semen than he would if he had been masturbating frequently. So you can say that if a man has not masturbated or had sex for a long time that his cock has a large supply of juices- this is known as having a juicy cock.
Man 1: Boy I've had no action in ages, I've got such a juicy cock.
Man 2: I could help you with that ma brutha.