PLT OF AN SMT TURBOPROP TAXIED OUT OF PARKING WITHOUT LOOKING FOR OTHER TFC RESULTING IN A CHALLENGER JET TAXIING TO STOP ABRUPTLY IN ORDER TO NOT COLLIDE WITH THE RPTR.

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ON THE RAMP FOR 2 HRS BEFORE DEP; I BECAME ACCUSTOMED TO TFC MOVEMENT; OBSERVING THAT SOME OF THE ACFT WERE MARSHALED AND OTHERS NOT. AFTER STARTING THE ACFT; I BUSIED MYSELF WITH PLUGGING IN A NEW HEADSET. I CALLED GND AND RECEIVED TAXI CLRNC. THINKING THE RAMP WAS CLR OF ACFT AND NOT EXPECTING TO BE MARSHALED; I LOOKED STRAIGHT AHEAD AND BEGAN TO TAXI -- RIGHT IN FRONT OF A CHALLENGER JET THAT WAS APCHING FROM MY R. PAX SAID THAT IT WAS CLOSE AND THAT THEY HAD CALLED OUT TO ME -- I DIDN'T HEAR THEM NOR SEE THE JET. THANKS TO THE QUICK ACTION OF THE JET CREW; BOTH AIRPLANES AND MY BUTT WERE SPARED -- THIS TIME. WHY DIDN'T I LOOK BOTH WAYS BEFORE PROCEEDING? I FELT TUNED INTO THE RAMP OP; WAS PREOCCUPIED WITH A NEW HEADSET. PAX OFTEN ENGAGED IN RAUCOUS CONVERSATIONS AND SO IF I DID HEAR THEM I IGNORED THEIR ALERT. CORRECTIVE ACTIONS: 1) SHOULD LOOK BOTH WAYS -- ALWAYS -- BEFORE PUTTING AN ACFT IN MOTION REGARDLESS OF WHAT I THINK IS GOING ON. 2) PAY CLOSER ATTN TO PAX'S SIGNALS. I SURE HOPE THAT IT IS A LONG TIME BEFORE I DO SOMETHING THIS DUMB AGAIN!