Jordan and Nick first discuss Jordan's careless driving in chapter three when Nick tells her, "Either you ought to be more careful or you oughtn't to drive at all." Jordan's response is that she is safe because other drivers are careful and "it takes two to make an accident."
Later, in chapter nine after the death of Gatsby, Nick breaks off his relationship with Jordan. Jordan compares Nick's treatment of her to being "a bad driver" and admits that she thought Nick was "an honest, straightforward person." Though Jordan herself is "incurably dishonest" in their relationship, she is angered when she feels that Nick has been dishonest also. She is, symbolically, a "bad driver" who has just encountered another "bad driver" on the road of love.
Jordan believes that she has encountered another bad driver because nick dumps her without any warning. He calls her out of the blue and breaks up with her. She thought that nick was very cautious but that call angers her and she believe she now has encountered a bad driver in her life.
Jordan thinks Nick as careless as she is for starting a relationship and then breaking it off without warning. She doesn't see that her behavior is the reason that Nick doesn't want to spend any more time with her but assumes he is acting as reckless as the rest of her crowd.
Fitzgerald uses this to reinforce the lack of personal responsibility motif of each of the characters in Daisy's circle.