What is un-American? Is it difficult to define? Who gets to decide what un-American Is?

I believe being un-American is disobeying the law of America. In America there are laws that people have to follow if you’re American or not because you can be an American or Tourist, but no matter what since you’re in America you need to obey the laws. If someone decides to go against what the law is today with or without a citizenship in America, that is what i believe is called un-American like. I don’t think there is a particular defintion of being un-American only because it is not anyones choice to call someone un-American. I don't think anyone should have to right to do that because nobody owns American by themselves so why should they make that word a way to hit someone. I believe another word that is similar to un-American is Ignorant because going from my explaining of un-American i think its just trying to disrespect a country.