Well, I guess you can... if you have no class or couth.
An Issaquah, Washington bus driver (her name is something like Stacy Levanic or Lenovic?) was fired for flipping the President the bird. This wasn't a "free speech" issue...she has students in her bus that were waving to the President and he was waving back. Dubya took it in stride saying to his companion, "That one's not a fan."
The 43 year old bus driver then bragged to everyone that she had given Bush the finger. She was rightfully fired.
"A school bus driver, whose name has not been released, was fired for allegedly flipping her middle finger at President Bush's motorcade with students aboard last June. This week, according to an AP report, the woman filed a union grievance to get her job back.
According to one school district spokesperson, Sara Niegowski, "The bus driver was not terminated for making an obscene gesture at the president. The bus driver was terminated for making an obscene gesture in view of the students. That's not the role modeling we need for our students." (source)
If my kids were on the bus and Clinton was in the motorcade...I would want the driver fired. That is not behavior becoming of a school representative regardless of who was in that car.