Pony has a problem with Johnny's idea to disguise themselves for two reasons:
1. **He doesn't want to cut his hair.** Ponyboy's hair is long and greasy, and it is one of the things that makes him unique. It is also a symbol of his identity as a greaser. When Johnny suggests that they cut their hair, Ponyboy feels like he is giving up a part of himself.
2. **He doesn't think it will work.** Ponyboy knows that the police are looking for them, and he doesn't think that simply cutting their hair will be enough to disguise them. He is worried that they will still be caught, even if they disguise themselves.
Here are two details from the book that support these reasons:
* **Ponyboy's thoughts on his hair:** "I liked my hair. It was long and greasy, and I was proud of it. It was one of the things that made me me." (Chapter 5)
* **Ponyboy's doubts about the disguise:** "I don't think it will work, Johnny. They'll still recognize us." (Chapter 5)
Ponyboy's reluctance to cut his hair and his doubts about the disguise show that he is a complex and thoughtful character. He is not just willing to follow Johnny's lead without thinking about it. He is also aware of the risks that they are taking, and he is worried about what might happen to them.