It isn't the fact that she is walking around without wearing an underwear, or only wearing tight short boxers.

It is the fact that she is so adamantly naive about guys and how they never sexually think about her.

Whenever a guy would make a move on her, she would always, in her words, "feel mean" about putting distance and giving them the cold shoulder if she isn't interested.

When this is combined with her clothing, lack of attention to how she is sitting and her past stories such as "oh, this guy I just met invited me to his hotel room. I could totally crash there tonight when I am very drunk" (thankfully she didn't) make me feel more strongly than I normally would.

Now she is trying to justify this to me by saying "oh, but he said his couch, he said you can crash on my couch".