How to NOT be nice?

I'm too nice, to the extent that i can't live anymore. I consider people's needs before mine and expect them to be that nice back but rightfully tho they never do. I wish i just not give a sht anymore about anyone but myself. I feel like people are very opinionated, they want every little thing to be their way, if i want to do my own things my way they have a problem, and I'm just too nice to tell them off. I don't want people to assume I'm naive bc i choose to not give much thought about being selfless when i can. I want all of this to stop, i want to be a selfish respected person. How can i do that in the most simple yet effective way?

How to NOT be nice?
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