This friend will always suggest that you make the best decisions in life. Don't go out late at night, study hard (not the night before your exam), sit straight, stop having so much junk food, and do not get into trouble – whether you're annoyed or they're mad at you – this is the friend who'll always have your back and has the keys to your guilty conscience.
This just does not refer to the pretty girls in the group. S/he can be the pessimist in your circle, the attention seeker, or Blair from Gossip Girl (xoxo). Throwing tantrums, criticising people and/or things, creating drama through breakups, this friend of yours might just as well remind you of Donald Trump. But s/he somehow gets away with it, because your other friends put up with it, even though these “yuuuggee” problems are just minor issues.
This person just cruises through life with the minimum amount of investment. S/he will never be present when you're planning something new, but you can be certain that you'll be “blessed” with his/her presence there; even though s/he always ends up losing his/her wallet, or will definitely need to hitch a ride with you. You basically have to do EVERYTHING for this one.
The smartest one in the circle, that you respect a lot but have to constantly make fun of.
These people can do whatever they want to do on whatever day of the week, yet they are still focused on school and acing all the exams.
The Lovable Jerk
Whenever you think of this friend, you can't help but sing that song by U2 - “With or without you, I can't live, with or without you..” This friend or troublemaker can be a pain in the butt to other people and of course, you. However s/he happens to be the most loyal in your group and will be the first one to be there for you, even if you need some help at three in the morning, so you can't help, but love him/her (or otherwise, douchebags).