EMB145 CREW CROSSES HOLD LINE WHILE WAITING FOR CLRNC FROM TWR AT DFW.

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WE WERE CLRED INTO POS AND HOLD ON RWY 17R. A B757 HAD JUST DEPARTED. I STARTED THE TIME WHEN THE B757 STARTED ITS TKOF ROLL. TWR THEN CLRED US FOR TKOF 1 MIN 20 SECONDS AFTER THE B757 BEGAN ITS TKOF. I TOLD THE FO TO TELL THE TWR WE NEEDED A FULL 2 MINS. I COULD NOT SEE THE DISTANCE OF THE B757 ON THE TCAS BECAUSE THE SYMBOL FOR THE B757 WOULD APPEAR AND THEN DISAPPEAR ON OUR TCAS SCREEN. AFTER THE FO TOLD TWR WE NEEDED THE 2 MINS HE GOT IRRITATED AND TOLD US TO CLR THE RWY TO THE L. HE SAID NEXT TIME WE NEED TO TELL HIM WHEN WE WANT THE FULL 2 MINS. I GOT IRRITATED BECAUSE HE WAS TRYING TO CLR US FOR TKOF 40 SECONDS EARLY BEHIND ONE OF THE WORST WAKE TURB ACFT IN THE INDUSTRY. THEN AS WE TAXIED CLR HE ASKED US IN A SARCASTIC VOICE IF WE WERE READY TO GO (HE HAD GIVEN CLRNC TO AN MD80 TO TAXI INTO POS AND HOLD; WHICH I THOUGHT HAD BEEN CLRED FOR TKOF). MY FO TOLD HIM WE WERE READY AND THEN I KEYED THE MIKE AND TOLD HIM THAT WE JUST NEEDED THE 2 MINS FOR WAKE SEPARATION AND THAT IS ALL. WHILE I WAS TALKING TO HIM I LET THE ACFT ROLL ABOUT HALF A PLANE'S LENGTH PAST THE HOLD SHORT LINE THINKING HE HAD CLRED US INTO POS. THE FO DID A GOOD JOB AND GAVE ME THE HEADS UP THAT WE WERE NOT CLRED INTO POS YET. OUR POS IN RELATION TO THE MD80 WAS WELL BEHIND HIM AND AT NO TIME DID WE EVER CAUSE A CONFLICT WITH HIM. AFTER THE MD80 WAS CLRED FOR TKOF WE WERE GIVEN INSTRUCTIONS TO TAXI INTO POS AND HOLD. I BELIEVE THE EVENT OCCURRED BECAUSE I LET THE TWR CTLR GET TO ME. I WAS TOO CONCERNED WITH WHY HE WOULD TRY TO CLR US FOR TKOF THAT CLOSE TO A B757 AND WHAT I COULD SAY TO HIM THAT I LET IT INTERFERE WITH THE JOB AT HAND.