I would have to say when I was bullied for two years in middle school. I had a couple of friends but they were in other classes. As a result I was essentially isolated from the rest of my class who bullied me daily, escalating to physical violence now and then. I'm still feeling the psychological effects even now (Depression, Social Phobia, Panic Disorder, etc), 10 years later. It's not as bad as it used to be thanks to the other students at the Alternative School I went to years later, but still present.