From my experience and collective reading of all sorts of incidents, it seems to touch the car, even if not intentional is when all hell brakes loose. I once had a guy cut me off by speeding up and making a right on red without stopping while the light was changing, other cars were stopped and I was making a left through the intersection and had to get out of the intersection. Right after cutting in front of me he has to slam the brakes for a truck pulling out forcing me to slam my brakes too. My front wheel barely taps his rear bumper, not even a thud, just a tap, and he pulls out of the car looking ready to start a fist fight yelling about how I was damaging his car (didn’t even leave a mark of dirt), never mind if I hadn’t reacted fast enough I could have got flipped onto his car. He calmed down, but to add to the awkwardness we both pull into the same building for work, and he works at the studio right next to where I do, about 2 blocks from the incident. He gives me this dirty look as I pull into the same parking lot. I later on a whim not really planning to do anything with the info, go and cell phone camera shoot his license plate and he sees me do it. Then suddenly he comes out all apologetic about the whole thing after that.