It appears to be a popular idiomatic expression, but with a much deeper meaning. The quote has a symbolic meaning of carelessness towards life from Jordan and other residents in East Egg. Besides, it is a foreshadowing element of the climax of the novel.
‘Either you ought to be more careful, or you oughtn’t to drive at all.’
‘I am careful.’
‘No, you’re not.’
‘Well, other people are,’ she said lightly.
‘What’s that got to do with it?’
‘They’ll keep out of my way,’ she insisted. ‘It takes two to make an accident.’
In this scene, Nick is condemning Jordan for her careless driving. The emphasis on “it takes two to make an accident” refers to the popular idiom “it takes two to tango.” Simply put, it means that any situation requires the involvement and action of at least two people. However, Jordan absolves herself of responsibility, which is inherently the metaphor. It is a typical attitude towards life from most East Eggers, demonstrating carelessness towards others.
“They’ll keep out of my way” is potentially meant as a joke. But it is a reflection of her arrogant belief that others must adapt to her desires. Jordan admits that she is careless, but she is shallow and superficial. So she will make the conscious choice to act this way. If an accident happens, she has the safety net of her wealth to protect her.
It is undoubtedly a foreshadowing of the climax of the novel. Daisy, being a careless driver, kills Myrtle Wilson in an automotive accident. Meanwhile, Gatsby is so infatuated with Daisy that he becomes complacent with her carelessness. And he helps her cover up the accident and takes the blame. As a result, Gatsby’s death at the hands of Myrtle’s husband is indirectly caused by Daisy’s careless driving. It creates a sad irony in the novel that was foreshadowed by this quote.