The sudden vitriol from Rose has Terezi's hackles raised as she stumbles back from the shove. It's a good thing that Dave is intervening because Terezi is more than a little defensive after that "greeting". She has no intention of attacking, but she's not just going to let herself be attacked, either. Her shoulders are hunched and ready for an attack, even as she gives Dave an equally confused expression in return for his.

"Wow, Lalonde. I am pretty sure that you are neither the boss of him or my hands, so consider your orders null and void! I will place my hands wherever I like." Which isn't to say that she's going to, that would be kind of awkward in their state of things, but Rose doesn't have any business telling her where to put her body parts.