Sirius could feel his hackles rise with every word out of Regulus' mouth. He wasn't here to fight with the kid, why did Reg have to make everything so hard!
"I wasn't the one who sided with Mother every step of the way, not to mention a homocidal Dark Lord!" He snapped his mouth closed, knowing he'd let more of that old pain out if he kept talking. Why did everything with Regulus have to be a battle? Why couldn't they ever just say what they meant?
Practice what you preach asshole. Je won't talk to you if you just yell at him.
"And okay, maybe you didn't actually die, but I thought you did and that was bad enough, okay? So sue me for not wanting to go through that again."