The greasers value being "tuff" in themselves and other people they admire. One reason they care about their hair so much is it is their trademark, and one can't be tuff without great greaser hair. Another element to being tuff is being cool and tough. The greasers admire Cherry Valance because she never shows any fear, even when Dally is harassing her. To show weakness or disloyalty marks one as a coward, thereby taking away the "tuff" title.
However, the greasers value loyalty above all else. Even when they might get into trouble, they still stand by the members of the group. For example, at the trial, Darry refuses to speak against Dally, even though his association with Dally could threaten his custody of Soda and Pony. As Pony runs toward the burning church, he finds Johnny right along beside him, even though the situation is highly dangerous. The greasers stick together because, without each other, who else do they have?