3. 'Seeing Red' (Season 6, Episode 19)
A seemingly typical Buffy episode – specific evil to fight, along with some soap-opera drama among Buffy and the Scoobies – turns unexpectedly heartbreaking in the last few seconds. Three high school classmates of the now-college-age Scoobies are bent on living out a real revenge-of-the-nerds scenario by stealing some magical orbs that impart strength and invulnerability. (The fact that the items in questions are "balls" isn't a coincidence; the entire episode serves as a brilliant critique of modern masculinity's dangers.) One of the villains comes to Buffy's place with a gun; bullets end up killing Tara, who's inside the house with her girlfriend, Willow. That such toxic dude-ness would ultimately take the life of the series' beloved lesbian-witch character was both ironic and, in its own horrible way, a perfect commentary on our destructive bro culture. Hers is one of the great deaths of TV history, with the fan uproar to prove it.