Am i that bad?

Two days ago, i had a (long) conversation over the phone with a friend. I can't say she didn't surprise me.

I mock people a lot. I like that. I do it very often. My friends are used to it. They know i don't mean to hurt them. I want us to have fun.
In my case, it's one way to prove others i'm interested in them.
I'm very different with people i don't like: much more colder.
And i'm fair: i laugh at others, i laught at me, as well. I do say i have a sense of humour. Trust me on this. I like when people mock me.

Anyway, she told me that, sometimes, i did hurt her. Though she knows i'm not serious when i say bad things about her, when i put some of her "bad sides" under the light, she did feel hurt.
I was so surprised. You may tell me i should know that...i don't.
I really do it very innocently. It's just fun, not much. I don't intend to hurt anyone.
She told me i must be careful sometimes, especially with new people (who don't really know me yet). I might never see them again.

She's spending this weekend with me. I promised i'd be more careful.