Harry was less affected by Greg's glare than his continued near-nakedness. It was far safer to focus on the glare, and he gave his own stern look back. "It would be quicker to do this here, Goyle. It's routine, at this point." He just wanted to get this over with, and he didn't need Goyle being difficult about things.
"Look, go put some clothes on and I'll wait here. We can do the interview in the hall; I don't have to come in unless there's traces of Dark Magic." Despite his dislike of Gregory Goyle, he didn't think this suspicious activity call would amount to anything. Even Goyle wasn't that stupid. "Or we can go down to the Ministry where this might take hours instead of twenty minutes. Your choice, Goyle."