This actually happened in front of my house. A FedEx truck was parked on the other side of the street, then a UPS drives up parks on my side of the street. They wave and the FedEx truck drives off.
I've witnessed the same thing here in the UK - Both drivers are under immense time pressure and could have over 140 deliveries a day so they empathise with each other and they took and wave - In today's world they are true heroes.