Is giving 1 week notice ok for a casual job?

I work in a seafood place as a casual person, and I really want to quit as people there aren´t nice. I haven´t work for the past week because I had to get surgery done. Is giving 1 week notice ok for a casual job, the thought of going back there backs me feel very sick and nervous. They can easily find another person to take over my shift I usually do as I only work once a week. Do I have to write a resignation letter and email it to my boss? I don´t really care if they get mad at me because I won´t be using them as a reference or anything.