From the ArcaMax Publishing, Jokes Newsletter:
http://www.arcamax.com/news/jokes/s-569798-915190
A man is driving up a steep, narrow mountain road. A woman is driving
down the same road. As they pass each other the woman leans out the
window and yells, "PIG!!"
The man immediately leans out his window and replies, "WITCH!!"
They each continue on their way, and as the man rounds the next
corner, he crashes into a pig in the middle of the road.