crossover

I really don't like when people take me for granted. At the moment, I feel that I have been taken for granted by someone. And it is not the first time...it's the second time. I wonder if this is about me or about her, so she can easily crossover me. I start to question myself if there is something in me that makes people easily take me for granted or it is, indeed, her personality.
Well, you can say that i am exaggerating, whatsoever, but that is exactly how i feel now.
The worst is, I don't know whether it is my weakness or there is something in her that makes me so...until now I cannot express it to her that I don't like her treating me that way.

Last night, a friend of mine told me that I have been playing angelic so many times to some people, that's why they then have the idea that whatever they do to me I will feel alright. She told me that once in a while I need to just express it openly if I don't feel okay about the way they treat me.
Well, I'm not trying to defend myself, but actually I already have done what she suggested. Though I admit that mostly I express my objection jokingly or implicitly. My friend said that it was not enough, coz reality speaks that these people (in this case is her) just do not get it. They didn't think that I actually really meant it. She said that I need to state it clearly in such a way so that they understand that I AM serious.
Another possibility, she said, these people indeed get what I mean but they just know exactly that I'm not going to let things go wrong as long as I have the capability to secure things. They know it and that's why even though they feel my objection they still think that in the end I will be okay.

Maybe what my friend said is right. I guess this is one of my weaknesses. That's why lately I've been thinking of having a new work environment...thinking that maybe things will go much lighter in a new environment with people other than the ones I meet daily now...
I don't know...