Your freshman roommate:
Introducing myself as your new roommate! Listing a couple very mainstream things about myself so you think I'm a normal non-weirdo and asking you to do the same. Wondering if you're going to bring a mini-fridge and microwave and resent me for using them and never cleaning them, or if I'm going to have to bring them and resent you? Also, asking when you think you're gonna move in so I can plan how to get there before you and get the better side of the room?
Hastily expressing excitement to make the rest of this message seem less annoying!
Your high school friend:
Hey! Pointing out how long it's been! Explaining that I thought I'd send you a Facebook message since I weirdly don't actually know your email even though we used to be close friends, because I never needed to email you when I saw you every day in high school. Asking how much you're LOVING your freshman year? Assuring you how mindblowingly amazing my freshman year is so profusely that I'm definitely lying.
Anyway, telling you that I just saw something that reminded me of a stupid inside joke we used to have and it made me think of you, so that you think that's why I'm writing you, not because I'm lonely.
Asking specific questions about your courseload/clubs/roommate so that you'll feel obligated to write back even though we'd both be happier if we just let this relationship die its natural death?
A douchebag you had one class with:
Just a reminder about MY AWFUL EVENT TONIGHT that you don't plan on going to and even if you did you wouldn't need a reminder about because Facebook already reminded you on your home page! Hope to see you there so we can use your $OVERPRICED TICKET MONEY to pay for the enormous venue we paid too much for!
Overly enthusiastic greeting! Explaining that I just thought I'd sending this as a Facebook message instead of an email to make it seem more casual and not like me asking you for a favor. Insincerely wondering what you've been up to without expecting a response? Asking how the significant other you haven't been dating in six months is doing?
Oh, by the way, framing it as an afterthought that the actual reason for this message is that I would like you to hook me up with a job/ internship//date with your friend/donation for my charity thing.
Thanking you even though you haven't agreed yet so now you have to do it!
Someone who has a crush on you:
Hey, question about the class we're in together that I don't actually need answered? Trying to flirt via Facebook message because I'm too scared to straight-up ask for your number and we only use each other's school emails so you don't show up on my gchat bar.
Joke about how weird our professor is, even though she's not really that weird, in a desperate attempt to find some common ground with you and to make this message long enough that you'll respond and we can keep talking and eventually drunkenly hook up.
[All of the above.]