"Jancok" is a Javanese-Indonesian curse word. It often used if something bad happened to the people who said it.
"Jancok! Motor gue mogok di jalan raya! Tolongin gue dong!"
"Jancok! My Motorbike suddenly breaks down in the road! Help me please!"
(The speaker talks with his friend on the phone)
It does not actually have any concrete mean, but it can be used to express anger to someone or something. Its usually used interchangeably with other swear word such as "Fuck"