RWY INCURSION BY AN ACR TWIN JET CAUSES THE GAR OF A C172 ON FINAL APCH AT SNA; CA.

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MIDDAY JFK OPS AT SNA. LOTS OF LIGHT ACFT TFC AND AIRLINER TFC FOR RWYS 19L&R. RWY 19L USED FOR LIGHT ACFT; RWY 19R FOR AIRLINERS. WHILE HOLDING ON TXWY A SHORT OF TXWY L; TWR TOLD US TO TURN THE CORNER AND HOLD SHORT OF RWY 19L. FO ACKNOWLEDGED THE CALL FROM TWR AND CONFIRMED THE 'HOLD SHORT OF RWY 19L.' I; HOWEVER; WAS THINKING RWY 19R. WE PROCEEDED ON TXWY L TOWARD RWY 19L; BUT SINCE I WAS THINKING RWY 19R; I CROSSED THE HOLD SHORT LINE FOR RWY 19L. THE FO RIGHTLY CALLED FOR THE 'HOLD SHORT' TO ME; AND I WAS STILL THINKING/CONFIRMING (ERRONEOUSLY) TO HOLD SHORT OF RWY 19R. THE FO; RECOGNIZING THAT WE WEREN'T ACTUALLY STOPPING; SAID 'STOP.' AT THAT POINT; I QUICKLY APPLIED THE BRAKES AND STOPPED THE ACFT ABOUT 20 FT BEYOND THE HOLD SHORT LINE. A LIGHT ACFT (A C172; I THINK) ON FINAL WENT AROUND; SEEING THAT WE HAD CROSSED THE HOLD SHORT LINE. TWR THEN CLRED US TO 'POS AND HOLD' ON RWY 19R. LESSONS LEARNED: 1) CONFIRM WITH THE FO THE ACTUAL TAXI/HOLD SHORT INSTRUCTIONS. 2) CHK FINAL APCH CORRIDOR FOR TFC. 3) CALL OUT SIMPLE COMMANDS LIKE 'STOP NOW' THAT DON'T REQUIRE FURTHER THOUGHT.