It is a term used by eighth graders to show their authority in the middle school. When one says "sevie", it is usually when telling someone something to do. Never a pleasant thing to call someone, but it sure is fun to get people to do whatever you want to do.
This term is almost never used by high schoolers, but pretty much always used by 8th graders.
8th Grader 2: It's alright just blame it on those sevies, who cares about them anyways.
8th Graders: Get off the back of the bus sevies!
8th Grader: Fuck you sevie just buy me some pizza.
Sevie: Whatever man why don't you just leave us alone...
8th Grader: BECAUSE YOU'RE A SEVIE!
9th-12th Grade Student:I thought your parents would have raised you better. You might as well drop out of highschool now and save them the money
"Isn't he the creepy one?"
"Yeah, well he's dating a grade seven!"
"That poor, Sevy"