Answer: when Neal chases down the taxi that Del had stolen
After Neal loses the race to the vacant taxi cab, he sees a man easily hail a taxi. He runs over to the man and asks him if he can tempt his good nature and buy it from him. The man not so generously agrees and makes Neal pay a pretty hefty price for the cab. As he is paying the man, Del and the taxi driver are loading up the taxi with Del's luggage. By the time Neal turns to get into the cab, it speeds away. Neal then chases the cab until he finally catches up to it and throws the door open to find Del with a frightened look on his face. He yells at him to get out of his cab, but instead the cab speeds off once again, leaving poor Neal in the middle of the street!