The main definition for an anti-twilighter would be someone who very much dislikes Twilight.

They are also the only hope left for mankind.
(Also see MLIA)

These people are most probably fans of Harry Potter, Google, and Ninjas.

A living, breathing human being, whom is obviously not a teenage girl, that dislikes a series of books called, "Twilight" by Stephenie Meyer. These idiotic humans usually verbally attack twilighters saying things like "Dude, Edward isn't real." Or "Dude, they're just books." Also, "Dude, Edward is a fag."
Anti-Twiligher men are often found dateless.

More commonly referred to as "Antis"

Usually seen as men, but are actually made up of a large number of teenage girls. Many were converted when Breaking Dawn came out. They are often attacked when voicing their opinions about the book.

They very rarely use force. Most are sane and tend to use logic. A lot condone the use of trolling on Twitard boards such as the Twilight Lexicon, but antis often do.

Anti sites, such as TwilightSucks.com, are often flamed by batshit insane fangirls for merely having a different opinion.

Most respect sane fans so long as the fans respect them. They don't respect batshit insane fangirls.

Most common arguments against Twilight include

-Edward is abusive
-Bella is antifeminist
-Pedophilia

Rational, normal human being who can't stand the ridiculous tween vampire series, "Twilight". Regularly laughs at both the teens, tweens and soccer moms who line up for every movie. Uses terms like "twitard" to explain to other, equally normal thinking people what these jagoffs are like.

A pejorative term referring to a rabid, obsessed fan of the Twilight series (a.k.a. twihard).

Unlike regular twilighters, twitards practically worship the series (some even referring to it as the bible) and refuse to tolerate any parodies or critiques of their beloved obsession.

Twitards are known for expressing their dislike of people who don't like Twilight (especially anti-twilighters) through the following:
-yelling or abusing caps lock/exclamation points
-cursing
-threatening
-violence (including, but not limited to, punching, beating, kicking, and fish slaughter)
-ad hominems (the most common ones being: "you're ugly," "you've never read the 'saga'", and "you have no life.")
-false statistics
-expressing their and their friends unending love towards the series
-horrifying spelling, grammar, and syntax