sadist

from WordNet (r) 3.0 (2006)

sadist
    n 1: someone who obtains pleasure from inflicting pain or others
         [ant: {masochist}]

from Moby Thesaurus II by Grady Ward, 1.0

37 Moby Thesaurus words for "sadist":
      annoyer, badgerer, bugger, bully, coprophiliac, erotomaniac,
      exhibitionist, fetishist, harasser, harrier, heckler, masochist,
      nag, narcissist, necrophiliac, nudnik, nudzh, nymphomaniac,
      paraphiliac, pederast, pedophiliac, persecutor, pest, pesterer,
      plaguer, rapist, satyr, scotophiliac, sodomist, sodomite, tease,
      teaser, torment, tormentor, transvestite, voyeur, zoophiliac