Well, since you're here, Miss—I mean, Little Sister, whatever you want to call her. Poor ol' Fatty Mengdie has no clue how old she is, but that's not the point. He just wants to tell Mengdie that you can scare folks to death showing up silently like that. Have some decency, will you?
Of course, all this is just Fatty's imagination running wild because he realizes he can't communicate well with this person, not like he would with others on this mech. Aside from Blade Warrior, it seems only Roland can exchange a few words with Mengdie. She doesn't get along well with others, and that certainly includes himself.
So Fatty ponders and overthinks, wondering with all his might—maybe for a split second or several. As thoughts tumble around, he finally sighs softly, "Hey, you..."
Mengdie clearly heard him, casting a fleeting glance his way without bothering to respond.