1. Childhood friends who you're not close to anymore
You like and comment on all of their statuses and photo albums because it's the only way you have time to keep in touch nowadays.
2. Family members
You're just hoping Aunt Jane doesn't see any embarrassing/non-PG photos you've been tagged in.
3. Classmates who will become really successful/famous
You try to stay in touch with them just enough so you might possibly be able to call in a favor with them when they become a movie star or CEO of a huge company or the U.S. president.
4. Work colleagues/friends from extracurricular activities
You make sure to tag each other in photos of club events or at work and are constantly messaging each other about who's bringing food to the next meeting or practice.
5. That friend of a friend whom you've never talked to
You're not quite sure why you're friends with them, but you need a few of these so you don't have a friend count as low as a hermit's.
6. Classmates who you have to do group projects with
You're only friends with them so you can easily nag each other about finishing the PowerPoint.
7. Your ex
You're not really sure if they count because you unfollowed them so you don't have to see photos of them anymore. But you didn't want to unfriend them outright lest you create drama.
8. Your crush
Despite your best intentions, you like every photo they're in and know everything about them...even though you two have barely talked IRL.
9. Summer camp friends
Every few months you stalk their profile to see what they've been up to.
10. Former teachers from middle/high school
You wanted to keep in touch with them but it's a bit jarring to realize that they actually have a personal/social life outside of school. They're probably thinking the same of you too.
11. Actual friends
They're the ones appearing in all of your photo albums, posting funny articles/videos they've seen on your timeline, and supporting you all the time, because that's what friends do.