While I think the bus driver's one-finger salute was disgusting and disrespectful, she should not have been fired over it.
As a few other posters have said, I might've been tempted to do the same had I seen BJC under the same circumstances.
She was representing a company at the time and there's rules. If she was in her private vehicle then I could agree with you.
And if you had done the same thing: flippin the bird while driving your employers vehicle, while being on the clock, and in front of your bus riders, you too should be fired.