Why is my sister so mean to me?

I am the middle child of 3 girls. All my life I have been ganged up on by my sisters. My 24 and 16 year old sisters get along better than I do with them. I am 20 years old. Over the years I have become closer to my younger sister but I feel left out everytime I get together with the both of them. I'm afraid I don't have much of an opinion of my older sister as she is a drug user and refuses to pay her bills. She is currently sailing on the ocean in a tiny sail boat from newyork to florida. Any how everytime I see her the first out of her mouth is a nasty comment towards me like my hair looks like crap and she questions my decisions about my life making me look stupid. I have always said nice things to her and was courteous to her. Because of this I dread and hate going to see her and sometimes I avoid it all together. Today I decided to go with the rest of the family to say good bye to her before her trip. I was dreading it and when I saw her the first thing she did was give my younger sister the biggest hug in the world and said to me I need to grow my hair out bc it looks like crap. The thing is I have gotten compliments on my hair and I thought it looked nice. I was very offended and lost my cool and I picked up a strand of her hair (which are dreadlocks she does not maintain- I have nothing against dread locks but her head looks like a rats nest bc she uses no product) and said, "My hair looks like crap?" She continued to ignore me most of the time when I was there and talked to my younger sister but when she introduced me to her boyfriends family she said "and this is my obsolete sister Leslie." I asked my dad if we could leave to go eat after awhile quietly so noone else would here and so noone would be offended. Unfortunately my sister heard and gave me a look and my dad repeated my question to her outloud. I was so embarred I looked like such an ***. I was so hurt by this that I cried all the way home when we left. Why is she so nasty to me? I have never done anything. Do you think it's maybe bc I have never gotten into serious trouble and am closer to my parents than she is? My younger sister says she is only joking. If so then how come the only phone calls I receive from her are ones where she berates me for a decision that I have made. It hurts when my dad says I don't know what is bothering you.