IFR DEP FROM BFI ATTEMPTED INCORRECT TURN.

Narrative

WE WERE SCRAMBLED FROM THE HOTEL FOR A FLT AND WE WERE ASSIGNED THE KENT 4 DEP FROM THE CLRNC DELIVERY. ON TAXI OUT; WE BECAME HURRIED AND OUR CRM SUFFERED AS A RESULT. WHEN WE WERE CLRED FOR TKOF; I THOUGHT THE TWR SAID TO TURN R TO 180 DEGS. THE COPLT DID NOT VERIFY THIS AND IT WAS SET IN THE WINDOW. THE KENT 4 DEP CALLS FOR FLYING THE RWY HDG WHICH WAS 130 DEGS. AFTER TKOF; I DELAYED TURNING TO 180 DEGS SINCE I COULD SEE SEA ARPT TO OUR R. I BEGAN A VERY SLOW TURN AS THE PNF CHKED IN WITH SEATTLE APCH AND SAID WE WERE TURNING R TO 180 DEGS. HE SAID THAT WE BETTER NOT BE AND GAVE US A HDG OF 090 DEGS. I DON'T THINK WE ENCROACHED ON HIS AIRSPACE; BUT I AM NOT SURE OF THIS. I WAS DISGUSTED WITH OUR PERFORMANCE SINCE WE SEEMED TO DO MANY THINGS CONTRARY TO SOP'S. YES; WE WERE TIRED AND HURRIED BUT THAT CAN BE NO EXCUSE. BOTH OF US (PLTS) WERE DOING OUR OWN THING AND CRM WAS NON EXISTENT. I FAILED TO REVIEW THE SID. THE PNF DID NOT VERIFY WHAT I THOUGHT I HEARD BFI SAY. THE NIGHT BEFORE WE ALL HAD ABOUT 3 HRS OF SLEEP AND WERE STILL FEELING THE EFFECTS OF THAT. IT WOULD HAVE BEEN BETTER TO SIMPLY REFUSE THE TRIP SINCE WE WERE STILL FATIGUED. WE LEARNED AGAIN HOW NOT TO OPERATE AN ACFT WITH 2 PLTS AND THANKFULLY THIS EXPERIENCE DID NOT CAUSE AN NMAC OR WORSE.