Argh...I Can Never Keep My Mouth Shut

WHY CAN I NEVER SHUT UP? I ALWAYS SHOOT MY MOUTH OFF ABOUT THINGS LIKE A BLOODY KNUCKLEHEAD. ARGHH!! AND IM USUALLY THE QUIETEST PERSON IN THE GROUP. WHY? WHY CAN I JUST SHUT UP AND THEN PEOPLE WONT HAVE TO GET PISSED OFF?!?!?!