To disidentify with something means to go against or disagree with the representation or stigma placed against whatever you define yourself as. I think in order to disidentify, you must first be able to identify. By this I mean, you must be able to have this self awareness of who you are and then decide if these social norms or rules places against that category represents what you think it should. If it does not, that is where one disidentifies.
Although I am female, I sometimes disidentify with it. I had many instances where I was expected to “act like a lady,” do houework, or dress a certain way. To many people this is what a female is supposed to committ to, but I disagree with it and therefore, push boundaries. I wear sweats and hoodies and sneakers almost everyday, I do things that my mother for example, would have never done at my age as a female. She would have never disobeyed her mother telling her to clean up while her brothers did absolutely nothing. I did not accept these norms, and I created my own.