The outsiders irony: a state of affairs or an event that seems deliberately contrary to what one expects and is often amusing as a result. p63 what's ironic about the hiding place in the country?

The line is spoken by Dally.  Johnny has just killed Bob in order to save Ponyboy's life.  The two boys know that they need to get out of town, so they go to Dally for a gun, money, and a plan about where to hide out.  During their conversation Dally scolds Pony for not thinking things through.  The exchange is ironic, because it is essentially the same thing that Darry said to Ponyboy earlier in the book.  The audience can see that Ponyboy may have turned his back on Darry, but the moment that he did Dally quickly fills that role with the same advice.  Ponyboy sort of sees the connection, but not clearly, which is why this scene is an example of dramatic irony.  

Explanation:

answer: you could try asking a family member maybe?