What do u think?

i guess romance is just not her field of expertise. I don't think she really is mad she just doesn't know how to express her affections for usui and uses the body language she IS good at: violence.

Cause he's a pervert and he teases her !!!

Part of it is that she is in denial about her emotions. She does not want to admit that the man who she previously despised, whom she has labaled as perveted and inhuman, could possibly have become someone whom she loves. Also, part of is habit and part of it is her attemps to keep her self-image of hating men and being all strict and cold.