Sirius had let Marlene go to show off her costume to a few others, no doubt it would be a lot like her birthday party and she'd end up making the rounds through everyone at the party. She did make the party a much better looking place though. He was looking for Jamie who was no doubt also making the rounds, when he happened upon an amusing sight, and after the announcement Sirius just couldn't let the opportunity pass him by.
"That's quite a costume you have there." He said raising an eyebrow as he sidled up to Snape, a smirk on his face. "Though I think the hat puts it over the top." Not saying anything about the additional facial hair Snape was now sporting, it would be too easy to do it all at once after all, he had to space these things out.