It depends on the girl, and the situation.
I had a girl complain that she thought I was freaked out by her touching me; when really, I arched away from her because she spilled scalding hot coffee on the back of my shirt, and it was hot! So my back stiffened a little from her, not because she was touching me, but because it was burning hot coffee on my back, and a drenched, icky coffee on my shirt.
There's a girl I used to like, and she'd come up and do this little weird quick back rub thing. Part of me LOVED it, but part of me would tense up because if I showed too much interest, or that I liked that, she'd have freaked out, and I didn't want to fall too hard for her by confusing a back rub with interest.