A B1900D CAPT TAXIING FOR TAKEOFF DEVIATED FROM THE CLEARED TAXI ROUTE AND CONFLICTED WITH AN MD-80.

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WE WERE CLRED TO TAXI TO RWY 17R FOR DEP VIA KEH. AFTER XING THE Y INTXN ON TXWY K; THE TXWY SPLITS AND TXWY K IS TO THE R. THE CAPT TOOK A L ONTO TXWY J. I EXPRESSED MY OPINION THAT WE SHOULD TAKE THE R SIDE. THERE WAS AN MD80 AHEAD OF US ON TXWY K AS WELL WE SHOULD HAVE FOLLOWED HIM. THE CAPT BEGAN TO TAXI PAST THE MD80 ON OUR R. AT THIS POINT I BECAME EVEN MORE CONCERNED BECAUSE WE WERE PASSING AN ACFT; WHICH WAS ORIGINALLY AHEAD OF US FOLLOWING OUR ASSIGNED CLRNC RTE. I ONCE AGAIN EXPRESSED MY OPINION THAT WE NEEDED TO BE ON THE TXWY TO OUR R BEHIND THE MD80. THE CAPT CONTINUED TO PRESS FORWARD ON TXWY J TRYING TO PASS THE MD80. NEAR THE END OF TXWY J HE STARTED TO TURN R TOWARDS THE RWY. AT THIS POINT THE MD80 WAS MOVING UP ON TXWY K ALONG HIS CLRNC. I SUSPECT HE THOUGHT WE WOULD BE STOPPING SINCE HE WAS FOLLOWING HIS CLRNC. AS WE GOT CLOSER I TOLD THE CAPT MD80 WASN'T STOPPING AND THAT HE SHOULD STOP. WHEN THE CAPT REALIZED HOW CLOSE HE WAS TO CUTTING THE MD80 OFF HE SLAMMED ON HIS BRAKES. AT THAT POINT THE MD80 HAD ABRUPTLY STOPPED AS WELL. WE THEN PROCEEDED FORWARD AND WERE CLRED FOR TKOF. WE ENTERED THE RWY AT EF AND DEPARTED RWY 17R. PART OF THE CONFUSION WAS THAT WE WERE ON TWR FREQ DURING THIS TIME. IT TOOK ME ALMOST THE ENTIRE WAY UP TXWY J TO CONVINCE THE CAPT HE WAS ON THE WRONG TXWY. NEAR THE END UP THE HOLD PAD AREA WE CAME ACROSS A TAXI SIGN WHICH VERIFIED US ON TXWY J. ONCE THE CAPT REALIZED HE WAS ON THE WRONG TXWY; HE SHOULD HAVE BEEN WILLING TO CORRECT HIS MISTAKE AND RETURN TO TXWY K BEHIND THE MD80 THAT WAS ORIGINALLY AHEAD OF US. HIS CONTINUING TO TURN AHEAD OF THE MD80 IS WHEN SAFETY BECAME AN ISSUE. QUITE FRANKLY I WAS JUST ABOUT TO THE POINT OF STOMPING ON MY BRAKES DESPITE HIS CTL TAXIING THE ACFT. IN HINDSIGHT I LEARNED I SHOULD HAVE JUST CLARIFIED OUR POS WITH TWR MYSELF OR RETURNED TO GND TO OBTAIN A DIFFERENT CLRNC.