It's a who.

[Yuffie's still pissed off with no clear direction, and her voice is still set higher.]

He's- He's [She makes a horribly irritated sound, and then because she cannot deal with this, she just promptly sits down in the doorway, legs crossed and her tea mug in her lap. She is equally not sober enough for this shit.]

.....I dunno what he is, but he's the literalworst.

[She seems to be more confused than irritated now, and she probably looks ridiculously childish.]

Whoever he is, I don't like him, and I don't think Cloud did either. He was being a dick.

[Things that Yuffie Kisaragi will later mark as understatements of the century.]