I wouldn't say that I thought about "giving up" on life. It was more that I thought everyone had given up on me, that they wouldn't care if I was alive or not. I wish I could pinpoint one time in my life when I felt this way, but to be honest it's how I spent most of my adolescent life. I've never been that popular - I was always outspoken and overweight. My fluctuating hormones didn't help much either.
It wasn't until the end of college that things got better. Even now I still struggle with self image. But unlike then I now have people I can count on and people who depend on me.