Sirius pushed the Fat Lady's portrait back into it's place on the wall, and brushing a few strands of hair from his eyes, he made his way through corridors and down the stairs. He wasn't quite sure exactly where he was headed, but he figured that Peter might've headed outdoors. To visit Hagrid, perhaps?
Sirius reached the bottom of the stairs to then Entrance Hall and froze for a moment. The Hall was filled with students of all houses and years, but the only one that really caught his attention was the fourth-year Slytherin skulking in front of the great oak doors before him-- the very doors he needed to pass through to find Peter.
Sirius' eyebrows narrowed and he thrust his wand arm deep into his robes, pulling forth from them his wand, clenched tightly between his fingers. Swaggering slightly, he made his way across the crowded hall, stopping a few metres short of where his younger brother stood, arms folded across his chest, a slight smirk playing at his lips.
Regulus leaned casually against the doors and locked his eyes with those of his older brother. "Sirius..." He hissed, running his thumb along the surface of his wand, which was also clenched between tensed fingers.
"Get out of the way." Sirius snarled, giving Regulus' shoulder a rough shove away from the doors.
Regulus jerked away, his eyes cold, hard, and suddenly quite empty. "No." He replied, sounding surpringly stoic. His smirk broadened. "Watch yourself, dear brother. There are professors in this hall, and I shudder to think what the consequences of you and I getting into a fight right now might be." Regulus paused. "Although I daresay Mother would be delighted for an excuse to send you another howler, especially after I tell whichever professor catches us about how you attacked me unprovoked, and how all I was doing was defending myself... Come now, Sirius, who do you suppose they would believe?"
Sirius growled, his eyes flashing malice at his younger sibling. "Shut up you bloody little b*****d- and- I- said- MOVE!"
With each word, Sirius pulled Regulus away from the door and shoved him roughly to the floor as he flung the great oak doors open, allowing them to slam loudly behind him. With that, he strode away toward Hagrid's cabin, utterly lipid and seething with rage.
Regulus merely scowled and picked himself up off of the ground, muttering furiously about how mother was most certainly going to hear about this. Ignoring those around him who were staring, or worse, laughing at him, Regulus turned his nose to the ceiling and strode toward the dungeons in what he thought was the most dignified manner he could muster, under the circumstances. As soon as he had passed through the threshold into the dungeons, he quickly put on a burst of speed, sprinting all the way into his common room and dropping lifelessly into the nearest armchair.
He rubbed his temples with his fingertips and groaned, his eyes shut tightly. Sirius was going to pay for that one...