From the Very Secret Diaries spoof of the Lord of the Rings
movie trilogy (Google it). Used whenever any of the characters start taking an unusual interest in Frodo/Merry/Pippin (but not Sam for some reason).
In the Real World, applies to anyone who thinks there's something going on between the onscreen characters.
Is meant to be used humorously.
SEE ALSO Shieldmadiens Gone Wild
Don't stare at Frodo too long. Sam will kill you if you try anything.