I hooked up with a girl a few months back. I had fun, but I assumed we'd never see each other again, so didn't respond to her text the next day. Well, turns out I did run into her, and she was miffed that I never texted her back. Was I being rude here or was she being too sensitive?
Well, a little of both. In not texting back, you were, in fact, communicating that you didn't want to communicate with her anymore. That's within your rights as a modern day hookup collaborator. However, a little extra courtesy padding should be applied when dealing with people we've seen naked. She was probably operating under different expectations than the ones you were, which is to say, maybe she thought you would see each other again. Maybe you thought “casual sex” and she thought “rapidly encroaching belief that I am going to die alone.” Maybe she just wanted to ensure that your walk of shame the next morning didn't result in you being stabbed. Who knows? Unless you explicitly said something like, “That was fun! What's even more fun, though, is knowing we'll never see each other again!” It's not out of the question to assume a night of fluid exchange might lead to other kinds of exchanges, sexual or otherwise.