Designating internal dialogue?

So, a friend of mine and I were just exchanging a couple stories, and, while looking at his, I saw an offset of dialogue in italics. I asked him what was going on, and he told me his MC is insane, and that he's having a dialogue with himself, in his head.

I told him I'd find out how to designate this, and, after ten minutes of troublesome brainstorming, I have nothing. Any suggestions?

Thank you! He had the entire thing italicized, which was throwing me off. This should help.