I can only recall one event in over 20 years, and I can't judge if it's intolerance or discrimination or just plain belief in something different by the other person.
I was in a small town in northwestern Nebraska, going for an MBA from a small state college so that I could keep legal immigration status. I was renting the basement apartment of a sweet 80+ year-old lady. Her son-in-law would come in periodically to do repairs. He was a slight man, soft-spoken, not threatening at all.
One time, he came to repair something and engaged me in conversation and asked if I were dating. I was, so I said yes and he asked if the guy was American and I said yes. And then he told me about God not wanting races to mix, and that's the reason why there were all these geographical obstacles--mountains, rivers, oceans, etc. (Silently, I was trying to decide if I should ask him why God allowed us to invent carts, cars, planes, trains, etc. but I decided to just let him go on.) He went on about what would my then-BF's and my offspring be if we had one. (Human?) Then, he rhetorically asked if there were species of animals that mixed, and truly not knowing much about biology as a business major, I said what about dogs? I can't recall how the conversation ended but eventually he went away.
My then-BF was steamed when I told him about this, but I dissuaded him from talking to the guy because the sem was ending and I'd be moving out anyway. Also, I just started thinking of what an uncle of mine would do in such a situation. (I look up to this uncle.) I decided that he would kind of think "I am glad that I know better than that man."
Other minor intolerance I've encountered were just in the form of comments not about me but other officemates from other countries who'd bring food for lunch that smelled a little stronger or fishier than standard American fare. I would always feel uncomfortable even if I were not the subject because I was a foreigner, too, and loved strange, smelly food. I remember my aunt from the US visiting us in the Philippines when I was just a child and still living there. She announced that Americans are very sensitive to smell. Our neighborhood in Manila was (still is) a hodge-podge of smells that our noses had become desensitized but here in the US, there are not very many bad smells.
So, there you have them, my intolerance experiences--intolerance of racial intermixing and intolerance of smells.