Well I will attempted to decipher the deeper parts of this song though of course I don't claim to know exactly what she felt.
I come from a slightly different background but my youth was tough and because I worked all the time outside of school and and was even kept out a lot to work it was hard to keep friends since I could not do much with them and was missing at school about a third of the time. I was smart and confident in what I knew.. I got along with the "cool crowd" and probably could have hung with them. I was mot ugly though my family made me feel like I was and made me feel worthless more that anyone at school did. But I think that I felt about the Cool crowd like I think Janis did. It did seem nice in a way but really i never wanted to be one of them.
She speaks of the debt they take on but will be unable to pay.. They started dating and making out and some even having sex in seventh grade. All the boys dated all the girl and vice versa. I though what will it be like later if they marry and they all slept with each other's spouses.?!! They show women and men lose the ability to pair bond after just 3 mates though men can recover more than women. That is a debt they carry. I won't speculate on STDs.
All they ever seemed to talk about was how great the last party was and how great the next one would be.It seemed so shallow to me. I didn't need drugs and alcohol to enjoy myself. I knew the wife swapping and cheating all that stuff that went on in town by the respectable people with professions or businesses. I would rather be a lone than be part of the fake shallow happiness they pretend to have. I would rather respect myself and honestly I'll take my lonely youth to that and their life after school anytime. I think that is what she was saying to those who can see the reality of they they envied at the time .