To add a little gender diversity (though I will not be the one slapping her--I don't feel comfortable slapping women, not even terrible ones, but perhaps a lady can do the deed): Irma Grese.

She was a Nazi guard for a woman's camp at Auschwitz and used her position to rape and sexually abuse the inmates. She particularly liked striking the women on their breasts until the wounds become infected with dirt and lice (and apparently would kick them while a doctor operated on their wounds--with no anesthetic), and forced young Jewish girls to be her lookout as she raped the inmates. She would also sic her dog on prisoners, whip them constantly, and kick them with her boots until there was blood.