Subject: Found one.
Author:
Posted on: 2013-04-24 04:50:00 UTC
It's not technically vampire!Frodo, but he does develop a hunger for Sam's blood because of a poorly described reaction to... something. Maybe the Ring, though it really never says. The writer appears to have a grudge against the poor spacebar, and during the story creates the mini-Balrogs "hoobit" and "Strangely Gollum", as well as a version of Sam that is only a bit disapproving when blood-drinker!Frodo goes ballistic and slices at him with Sting to get his blood.
It's no legolas by laura, but I had a pretty specific category to look in, and either way, it's definitely badfic.