From the Very Secret Diaries spoof of the Lord of the Ringsmovie 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.
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Don't stare at Frodo too long. Sam will kill you if you try anything.