The worst years of everyone's life. Not one person looks back on them fondly, even the people who were supposedly "popular" at the time. Typically middle schools offer 6th, 7th, and 8th grade. Some school districts like to be nice and have middle school start at 7th grade, thus making you only have to suffer two years of hell, but some like to be evil and add 5th grade to middle school, therefore making you have to sit through 4 years of misery, competition, and having to deal with not only your pubescent suicidal self who is a bitch/asshole on the outside, but also with hundreds of other suicidal pubescent pre-teens who are bitches/assholes on the outside.
The reason middle school is so bad is basically because everyone is going through puberty, making them feel like shit. So right off the bat their life sucks. To make matters worse, many people in middle school turn into obnoxious wannabes who think they're 10 years older then they are to make themselves feel better. These people form fake friendships and cliques and then make everyone else compete with them because they think no one is cooler then them. So in middle school people also pretty much hate each other. Lastly, work in middle school can sometimes be even more then high schoolers and college students get, causing a great amount of stress.
Luckily, middle school does go by pretty fast, so then you get to go to high school, which is 10000x better then middle school (although still not all that great).
High schooler: So how's middle school?
Middle schooler: It sucks. Really bad. I wanna die. Really badly.
High school: Aaah, yeah. I used to feel like that in middle school. Just remember when middle school is done you get to go to HIGH SCHOOL, which doesn't suck...as much as middle school.
Middle schooler: :| *encounters great amount of stress and hatred in the meantime*