Ponyboy is a deeply reflective and artistic person, and he thinks deeply about topics such as these. He is frustrated by his "station" in life, because he knows that underneath, he is much more than what his physical appearance and reputation might suggest. Ironically enough, the Curtis brothers were living a fairly convention, middle-class life until the loss of their parents; the oldest brother Darry was a good student and football star at the local high school, with a promising college career in front of him. Ponyboy, the youngest, is interested in books and writing, is a good student, and has none of the tough-guy personality that his appearance might suggest. This comment reflects his frustration about the social groups that define kids his age; he is well aware that the group known as the "greasers" is really the only family he has. To reject them is to be completely alone in the world, yet associating with them has created a reputation for him that is not authentic to the kind of person he really is.
Although most of Pony's greaser pals had high hopes for his future, Pony didn't have the same confidence in his own talents. He saw little chance of rising above his own lower status in Tulsa society, and college must have seemed a distant impossibility. It left him little of which to be proud--his fighting skills and long hair were two things that could not be taken from him.
As an adult, my response to this comment is that Ponyboy should just get over it. He is, to some degree, putting himself in this box that he doesn't like. Sure, he has been dealt a really tough hand in life. But it is not necessarily true that there is nothing else for him to be proud of. People carve themselves niches that go beyond stereotypes all the time. He could have been the greaser who was really smart and people would have respected him.
I think that we often (and I think teens are more susceptible to this than adults) think that we have to be whatever society thinks we should be. But that's not so. A person does not have to let other people's stereotyping define him/her.
Ponyboy is reflecting on the injustice of a class-based society. Because he is working class, his pride in his class is tied to what seem like negative things. He cannot be proud of his parents, his wealth or his grades. He is not part of the upper crust of society where those things matter.
Ponyboy is right in expressing his dissatifaction with the world which he occupies. He is perfectly correct. A world where the only way he can distinguish himself is through the outer trappings of his appearance and which does not seem to acknowledge or have any interest in his internal character is not one worth occupying. However, I think that during the course of the novel, and particularly at the end, Ponyboy realises that he can reach beyond such narrow terms of objectification and identification and choose how he wishes to be identified. The writing of his story is one example of this, as is the way that looking at sunsets and appreciating them appears as a motif throughout the novel, and is indicative of a deeper and profounder character.