[ ... right, this happens. there's just a hint of surprise when she lets out her part of the marinette-meets-adrien-routine even though he's very much used to this, because that was a particularly strong reaction. then again, he did just kind of come out of nowhere and ask her a question out of the blue about something she seemed frustrated about, so that might've been on him.... ]

That's... me. [ is what he says after a blink, still slightly confused, before he moves on to a lighter: ] Sorry, Marinette, I didn't mean to surprise you. I was just walking by and recognized you, so I thought I'd say hello.

[ a pause. maybe a compliment would help relax her? and it had been on his mind since he saw her, so he adds in an honest: ]

Uh... I like your dress?