We use the term, much as it is described above, but we apply it to a much wider range of people.

A gloom cookie has everything it takes, except the ambition.
A gloom cookie knows what it wants but is afraid to stretch for it.
In short, gloom cookies are the punk ass kids who you become friends with because you see how incredible they are, but no matter how much you believe in them, or how hard you try to convince them, they are too comfortable being the gothy/punky/depressed being they are to ever try to be anything else.
In addition to being found at malls, they can also be found at poetry readings, coffee shops, and 24-hour eating establishments.