An anti-hero is a flawed hero, and therfore, much more intresting then the more traditional heros. They can be working on the side of good, but with a tradic flaw, or a horrible past, or for reasons that are selfish and not intirely "pure". They can also be working for the side of evil, but with hidden noble intentions, or other underlying complexities. These darker heros can be jerks, pathetic, hard, jaded, or mean. However, all anti-heros must have enought heroic qualitys, intentions, or strenth (physical including attracktivness or mental) to somehow gain the sympathy of the audiance. Mostly they are intriguing and can therefore can be very, very, SEXY especialy if you love bad boys (girls). Well known anti-heros include Batman (yay Batman Begins), Angle, Draco Malfoy, and well...Napoleon Dynamite (sorry not a hot example).
Hero: I see the brave, shinning, world of tommorow!
Anti-hero: You must be delusional... And your cape's on backwards.