Some girls wont be afraid to call you an *******, mean, or rude. Don't worry about it, as long as you're not any of these things. I've done small things, like refuse to help a girl do something, and she called me an *******. Later on I helped her on my own terms. I strongly doubt she actually thinks I'm an *******. She may gossip about me being kinda mean at times (which is good because that means she doesn't like it, which makes your 'nice' moments more meaningful to her), but I'm sure that she just simply thinks I have balls and am not afraid of saying 'no'.
If she doesn't 'like' that, or it shocks her, then that is a good thing my friend. Because, deep inside, women love that quality in a man as long as you're not a total douchebag (to where she can say you're a lazy ******* and truly believe it).
Really, do you think it's bad that your acts of slightly being 'mean' bother her? It's GOOD that she wants you not to be mean. When she asks me for help, she knows there's a chance I'll say no. I don't go around looking like a lazy bastard who can't be bothered to help anyone, cause I usually help everyone around me. Just not every single time, and not if I don't want to.
Be careful, though. The first time you get on her nerves for being a 'man' and saying 'no' and so forth, she may ****test you to oblivion by busting your nuts and finding things to make fun of you about. This happened to me big time one night.