Anla

Sirius is ultimately responsible for his own actions, but Snape did deliberately infuriate and taunt him. But, the two of them have so much history, so much hatred there. I often got annoyed with some of the adults for not being able to let go of the past, although I guess it's a believable thing and happens in the real world, too. Sirius I could see why he couldn't - for him, it really wasn't the past, not emotionally. He was stuck in Azkaban since right after James and Lily died, tormented by Dementors. He didn't have much time to assimilate and deal with what happened.