"Are you really going to go without asking me the question that you've been dying to ask me?"
"Well I'm not.... I haven't been dying to ask anything. I... N-no questions here, for Stiles. Nothing."
It's the classic room mates switcheroo in which case Stiles and Lydia accidentally assume their newest room mate is of the same gender. And everything's fine two minutes in, but three minutes and Lydia automatically knows that good terms is out of the option. Sure he was sarcastic and a dick and she could live with that (having a few snarky comebacks herself). Until he has sex with his girlfriend. When she's literally a room away. Wait. Did I say girlfriend?
"Sweetheart, I don't think you understand. I don't date. And you'll learn that in a couple minutes when the next girl shows up."