If I can suppose for a minute and borrow the naive interpretation of the First Amendment then we can say whatever we want (but strictly should not say under the fear of the authorities investigating you under the pretense of "reasonable suspicion") and not get in trouble. Does that mean I can say "FIRE" and not face scrutiny? Does that mean I can declare my allegiance to a terrorist organization and not face scrutiny? Does this mean I can spout out racism/nativism (whatever people call it these days) without scrutiny? These speech patterns causes concern of different proportions and depends on context.
If you posed to me the question "can you be arrested for saying a trigger word/phrase?" and I would say of course depending on the level of concern you have caused with your speech. Let's remember that the public sets the bar on what you can say without raising concerns.
Situation 1: If you are at an anti-racism protest and you are spouting your counter anti-racism beliefs to this massive group of people, you are causing a disturbance and will be removed (let's not add the possibility of inciting a riot if the group is rowdy already).
Situation 2: You yell out "I AM ISIS" either online or outside on the sidewalk? You've increased the probability of the authorities showing up at your door/in your face and getting arrested for public disturbance (especially if the community does not tolerate this speech) or whatever trumped up charges that can be made up while you are being investigated. Hell you can even be denied entry in to the country if you are an immigrant thinking you have free speech! (Constitution don't extend to immigrants, so it is not surprising that the US govt. acts "third world"-ish to them in this regard)
Situation 3: You yell out "FIRE" and no one is around to hear. Will you be arrested? More than likely not.
Let's go back to the First Amendment. It says is that Congress cannot ban speech nor should it disbar the public from engaging with it. Does this address that an individual cannot be deterred from causing disorder with their speech? Heck no.
Even without the First Amendment, people can say whatever they want to say. If whatever you say triggers the public or authorities then you will face consequences in that context (beating, arrest, etc.).
Summary: I think using the First Amendment as a clause for why I can say whatever I want is weak when you do not consider public and authoritative concern. Free speech is limited explicitly and implicitly via consequential deterrence wherever you go. Whether an individual restricts their speech in order to not face consequences is up to that individual. You cannot strictly restrict speech without taking air from a person.