Sirius rolls his eyes at Andromeda, and then looks at Lily with disgust when she also misinterprets what he's dong. It's a look he hasn't given her since their early days at Hogwarts when she used to defend Snape's behavior. Snape doesn't even warrant his attention. He holds his palm out and suddenly there is a second, identical vial in it. He tosses one of them, presumably the original one, more or less at Snape, grabs the broom where it's floating in midair, and apparates away.

He could have flipped everyone the bird, but that lacked the proper nuance.