The exact opposite of a Twihard. The average Twihater hates "Twilight" at least for its being a dreadful novel, or a little more passionately because everyone around him is going mad about it and the series is thus destroying the Twihater's social life.
If asked, the Twihater can give at least ten good arguments against liking "Twilight", including evidence for each point. He is also prone to attacking Twitards whenever possible, if for nothing else than their being around him and talking incessantly about Edward and Bella (both of whom the Twihater would readily massacre if that meant that there would be five minutes of peace). Unfortunately, the Twihater is a tragic species: Twitards are naturally too dumb to understand his arguments, and therefore all his efforts are in vain. He can be compared to a very smart fish dropped in the middle of the desert of ignorance.
Twitard: "OMFG, Edward iz lyk sooo hawt!!!1!"
Twihater: "Please, listen to me. You need to get rid of this unhealthy addiction. Stop talking about marrying fictional characters, you look like an idiot. This book doesn't even have a plot, and its grammar and vocabulary are appalling, and..."
Twitard: *shrieks v. loud* "OMFG, U luv Edward 2, duncha???2"