I think this point got a little lost amid the general fandom glee at Dominique and Vanitas bonding (or at least it did for me), but looking back at chapter 60, the implications that this scene has for Vanitas are fucking wild.
It's not the only aspect of her relationship with him, but a huge cornerstone of Dominique's feelings toward Noé is the fact of her absolutely massive crush on him. Like, as much as she's venting about how he frustrates her, Dominique's thoughts on Noé in this scene are the thoughts of a woman that is canonically in love with him. And Vanitas apparently thinks/feels the exact same way.
As their shared venting reaches its fever pitch, Vanitas and Dominique both reach the exact same ending point. Noé is stubborn and overly straightforward and unrelenting, and both of them feel helpless against it. And they say as much!
They say as much, and then they both cut themselves off and flinch away in the exact same way, as though they've said too much. They've revealed some deeper truth about their feelings and the ways that Noé's force of personality affects them.
Dominique reacts this way presumably because she touched a little too close to the reality of her romantic feelings for him. The thing cut off at the end of "Since he's like that, I—" is some expression of the depths of her incredible fondness for and attraction to him. And Vanitas apparently feels the exact same way as Dominique. He expresses almost the exact same outward sentiment and catches himself and flinches in the exact same way. So if Dominique is speaking here in (albeit frustrated) love, then what emotions is Vanitas speaking from?
Awww! Your mother is so cute! :) But yeah - the other funny part about this parallel is that this realization comes after Pen/Kurt decide - fuck it, I'm just gonna be me now and stop pandering to what people think I need to be. They come into their own as themselves and that's when Colin/Blaine sees them.