The last time I flipped the bird to a driver who cut me off got the guy really pissed. He sped away from the intersection, slammed on his brakes ahead of me and threw the door open shouting, "you better call 911 'cause I'm going to hurt you bad" or something to that effect. I rode a wide berth around him but he got back in his van and chased after me! Like, he lit it up - squealing the tires and all. I hammered it to the next street which was fortunately a one-way and guy didn't come after me. I looked back after like 50 meters or so and he was just sitting there in his van at the top of the street.

That incident could've ended so, so bad. Really trying to keep calm even in the face of blatent rudeness and dangerous driving. It's hard though.