I call it the "Road Rage Virus".
If someone does something stupid and you get mad, you may end up passing it on to the next driver by doing something stupid later on.
It then spreads onto the next driver, then the next, etc etc.
The taxi driver was quite correct, if someone tries to "infect" you just wave and smile and it protects you from the virus.
I have been on the other side and someone waved and smiled at me and I thought "Oh" and was dumbfounded. It also made me feel better.
So the best antiviral protection is a wave and a nice smile.