I'm cordial but I wouldn't tell them any of my business, wouldn't make conversation, I would just be distant. It also depends on who it is and why I don't trust them.
I act normal. I don't have to change the way I am. But what change is what I talk about in front of that person. Absolutely nothing personal, not even an opinion. Just stuff like weather, food, clothes, news... that's what I do at the place I work because of the kind of people they are.