Crazies.

Crazies got hit with a version of the virus that didn't kill them, but completely reduced their motivations to the lowest base desires. They still understand complex machines, social structures and numerous other complex concepts, but their motivation and long term planning has been severely curtailed. If a Crazy wants, and thinks he's strong enough, he takes.

Many of them will rape women without concern for any other competing crazies around. In fact they will often share victims. Torture and numerous other nasty hobbies are usually what they resort to after they've finished. (However, for the most part, torture has remained offscreen, and I'd prefer it remain there) Some of them enjoy laying devious traps, and think far enough ahead to plot out what a victim might do after a violation.

Fortunately most have had their sperm counts severely weakened by the plague. Almost no normal woman is in danger from being impregnated by a Crazy, but Roughly a quarter have enough of a sperm count to knock up the female player character if they come inside her.

The final definition of whether a character is a crazy or not comes down to whether they can control themselves in a sexual situation. Admittedly, the male player character crosses this line several times, and it is up to the individual author whether he crosses the line to truly become a villain.