Curate, connect, and discover
Snirius trope where after a 'prank', Snape kinda freaks out. For some reason, it hits a nerve, it hurts him. Cue Snape having a panic attack or on the verge of one, and Sirius stumbles across him. At first, he makes a joke or two, poking fun, but once he realizes how freaked out Snape is, he stops.
Snape tells him to go away, but he doesn't care. He sits next to him, walking him through breathing exercises, leaving after he calmed down.
Or
He doesn't leave after he calms down. He stays and realizes just how much damage he's doing, just how much this all affects him, and apologizes.
OR
James, Remus, Peter, wtv, someone discovers him helping Snape calm down, and continues to poke fun at Snape or something like that, and Sirius just tells them to fuck off, and then continuing to help him calm down.