The clues we have are: - angry veins on her hand - sweat beads on the guy's face - embarrassed face on the guy
From my deductive power I'm guessing:
1. He used the sock to clean up semen and she found it. 2. She found her sock in his room. 3. He tried to shoplift a sock from a store and she caught him. 4. He is a dirty boy who doesn't wash his socks and she is scolding him.
- I wonder whose socks are these~ *irony* - Na-Nanako-chan's, aren't they? *sweat* - That being the case that's a problem, huh... *burrows finger into his chest* - Problem indeed..
I don't know their background, or anything about the characters, but it sounds like Jealousy.