"Coffee?" No, wait. He wasn't interested. He was outraged. Really. He was raised to be polite though, and so he slipped the little tube into his pocket (at least then he wouldn't have to look at it). "No-- well. Er. Thank you. But I don't see myself using it in the foreseeable future." Which was probably too much information, in retrospect.
And really, he didn't want to know what Sirius' favorite flavor was.