Being nice to someone who has been nice to you is easy. Maintaining your own professional demeanor and calm in the face of a bodily orifice is much more difficult and a true test of your maturity.
Just because someone acts like a jerk doesn't mean the entire conversation following has to sink to their level. If it does, you have relinquished all power in the situation and allowed them to set the terms of the exchange. Besides, not getting P.O'd generally annoys them!
Thats why it would take place in the parking lot.
But hey you have your way I have mine. Im sure we both arrive at the same place. Just take different ways to get there.