How do I go about this situation?

I started working at a job about 6 months ago and have been told from my co workers and boss that I am hard working and reliable. The minute one co worker complain and implies that I’m lazy to my boss, he takes her side without asking questions. He recently just ask me do I not know how to do the job correctly? This co worker she is my boss favorite so he let her get away with everything and people see it but cant really do anything. I just feel like shes targeting at me and I don’t know how to defend myself if shes the favorite. The thing is that I didnt even work the shift and I told her that but she just accuse me of leaving a mess for her to clean up so instead of listening to me she went to my boss and he didnt give me a chance to explain myself. I have been told to stand up for myself, but that something I havent done before. When a job get toxic, I just quit.