Troubles with saying “no”

This might be my biggest struggle in social interactions. I simply can’t stand up for myself, even when I don’t like some phrases towards me or some touches, or my schedule at work, I keep saying to myself that it’s fine and laughing, instead of saying “I don’t like it, stop it”. And crying after that because of feeling really miserable and not being able to say anything. But I don’t have these problems with defending people I love, as my family or friends. I am ready to tear apart anyone who does what they don’t like or says something bad about them in my presence. So, maybe somebody knows any hacks or techniques of dealing with it easier? My psychiatrist says that it might have something to do with ADHD-provided anxiety. I didn’t start psychotherapy yet but this is the problem that concerns me the most.