It's me - you. Don't drop the note right away - check the attached photo of me (you) showing your butt on the bus. No you weren't drunk, it's just I - the future you proving you (me) it's just me (you) in the future. Well the future you (me), in the past actually.
So I'm writing you for somewhen in the future you'll have the opportunity to time-travel. You have to use that to travel back to 2012, and sabotage a Hadron Collider in Sweden. Google it, it was sabotaged in 2012. That was me (you). Or actually right now just me, you have to do it later on. That's why I'm writing now. I (you) saved the world. Or you just will - if you follow my instructions.
After that, you can spend the rest of your (my) life in Jamaica, living from your lottery prize money, like I'm doing it right now. But don't come to visit me - it would feel awkward.