By definition, a metaphor is something that offers a comparison of two, seemingly unlikely things, without using the words, 'like' or 'as'. In The Outsiders, metaphors are prevalently used.
One of the most memorable metaphors in the novel happens in Chapter Five, where Johnny and Pony are discussing their looks. Pony quipps about their appearances being a Halloween costume that neither he nor Johnny can remove. Johnny retorted with
...it's our looks or us
In the above metaphor, Johnny compares their Greaser look with their lives in general. This metaphor speaks directly to one of the central conflicts in the novel, person versus self. By making the statement, Johnny also asserts that the boys can be separated from what they represent with their looks.
Another metaphorical example occurs again in Chapter 5 as Pony explains his understanding of the gang. Pony states,
Dally was real.
This metaphor must be explained in the context of the story. Immediately preceding the above quote, Pony explicates that he finally understands Johnny's "hero-worship" of Dally. He then goes on to compare Soda, Two- bit, and Darry to the heroes in the novels that he reads. He acknowledges that those guys all have shining, somewhat fictional, qualities about them. However, Dally represents the reality that scares Pony. He represents the reality that Pony often wants to escape in his reading of fictional heroes.
Another example of a metaphor in the novel comes from Chapter Six, as Pony describes Johnny's features and what makes others drawn to him. He states,
I don't know what it was about Johnny--maybe that lost-puppy look....
This metaphor compares Johnny to a lost puppy. If you are a dog lover, you get the reference. If not, this metaphor essentially shows Johnny's sweet, innocent, and engaging appeal--which draws a person into him--and makes them want to take care of his needs.
The last metaphor I'll discuss is one of the more famous lines from the book. In this line, Johnny is in the hospital about to die, and he tells Pony to "stay gold." The metaphor is comparing Pony to the value of gold. It also makes a loose connection to the book's consistent references of gold being favorable, desired, and authentic. Thus, Johnny has attributed all of those qualities to his friend Pony. He believes that Pony is invaluable, desired, and authentic. He wants Pony to understand that about himself, and recognize his own, inherent worth; both as a person and as a member of the Greaser gang. The metaphor is also an allusion to a Robert Frost poem which denotes the beauty of nature as being gold. It helps to consider how Pony sees sunsets, and the value that he places on nature alone. Then, consider the images of sunsets as you consider Johnny's request for Pony to stay gold.