Why doesn’t anyone believe that I’m going to beat someone up or handle conflict?

My family know me as the “nice” girl. The nice girl that helps people a lot, gets pushed around, a pushover, a coward, weak, and has no self respect. I also was told I’m WAY too easy going that people take advantage of me and let people talk to me disrespectfully. People purposely got into my face and push me around to get a reaction from me. I also let my cousin and kids and teens push me around and beat me up. I was too scared to fight because I was afraid to get hurt. I let people take my things and I just cry and let it go.
Even my best friends don’t believe I will fight because they know my weakness. They get fed up when I let people push me around but I don’t do NOTHING about it.
When I said I will fight someone that does this or that, my brother said, “No you’re not. You’re just going to let them push you around like you always do. I don’t believe you at all and your not being honest with yourself.”