Sadism - originates from the Marquis De Sad, a sexual torturer who was uncovered as having placed women in a dungeon and raped them while inflicting pain upon them. To be a sadist is to enjoy inflicting pain onto others in a sexual way.
Masochism - to enjoy being on the recieving end of sadism. masochists love being whipped by crazy dominatrixes or freakish gang rapists.
gah! Don't stick that whip up my ass you crazy sadist!