Dear HS self: There are two reasons you have no girlfriend: 1. no confidence. 2. poor hygiene. #startwithnumbertwo - John Green
Dear HS self: You are NOT FAT. You will be, but you're not now, so enjoy it. - Sara Zarr
Dear HS self: Facebook will be invented. Are you sure you want your friend to take that picture? - Julia Devillers
I first read about this on Dystel and Goderich Literary Management's blog - thanks, Stacey Kendall Glick!
As for what I would say to myself:
Dear HS self: You know that boy you love who broke your heart? He's gonna propose to you one day!
Now, dear readers, what would you say to your HS self?