One who takes fandom of Twilight, by Stephanie Meyer, to a level of or beyond obsession.
They often flames forum postings trying to defend the book, regardless whether the book was being critiqued negatively or not. They are also prone to using all caps, not checking their spelling/grammar, jumping to conclusions, falling in love with Edward, and biting people's heads of for just saying they didn't like the book.
They're worse than a rabid fangirl or a Narutard: it's a Twitard.
usually (A) lonelygirls who think they haven't been understood or (B) normal girls that don't read too often
Jane: hey guys i need a book suggestion
Girl A: well you can read Twilight, a book about swirling emotions and true love that MOST of you IDIOTS dont believe in!!
Girl B: I L0V3 3DW@RD <33333 SUP3R HAWTTT!!!
Jane: what?
Bob: oh those are twitards, get away
Mainly a girl who is exceedingly annoying and is hovering around you while you are trying to pick up a girl at a bar, club, or other events (be it charity events, doctors office, the grocery store, party... we have all seen the overly drunk girl at a party on some guy who clearly does not want her). This girl does not necessarily have to be a friend, she just has to be annoying enough to ruin your game.
Nick: Dude, that bitch was such a twatacopter, she was just hovering around me the whole night as I was trying to pick up Emma
Harry: I know man, she was one of those drunk twatacopters too, just hanging off you you basically. Fuck, sorry man
Nick: Don't worry about it... maybe next time she just wont be there.