He exhaled when Snape moved nearer easing up that strange sensation of magic and wrong that seemed to happen whenever he moved a little further from him. Which was not ideal in the least. He didn't want Snape near him, he didn't want to be in the same room as him. There had been far too much bad blood in the past, and Sirius was still too near the loss of everything important in his life and though Snape hadn't been the one holding the wand that night, he still blamed him.
And then he mentioned Lily and James and all the morning slowness disappeared and Sirius was on his feet in an instance wand in hand as he shoved himself right up into Snape's personal space wand pressed into his chest. "Don't talk about them, don't think about them." He warned. It was one thing for Regulus to accuse him of choosing his friends over family, it was something else entirely for Snape of all people to accuse him of murdering his best friends.
"You don't have the right to say anything about either of them after what you did." Sirius wasn't sure whether he wanted to hex Snape or punch him, both seemed like the right move in that moment.