Scratch

Easy. It's a bug.

If you would like to do it yourself, do this
1) Make sure you have two accounts.
2) Log on your secondary account and go to your profile page (make sure your secondary does not have your main friended)
3) Open another tab (or window) on the same browser and log out (do not close the other tab/window)
4) Log in to your main on the new tab/window.
5) On the old tab/window (lol), click add to friends. Done!