im not sure. i think its because to have a mixed race relationship, you must be more open minded and liberal attitude towards sex than the majority of people in single race relationships. this is why people will assume the woman is liberal towards sex by having mixed race relations and therefore is a ****. also, what is said about certain sizes of white/black mens....things might imply a reason she might be going out with him, therefore she has a greater interest in sex than the average person. these are only possible reasons why. i dont know why most people will think this. personally i feel if i had a white boyfriend people would think this.
ok, forget the stereotypes. none of this explains why are mixed race couples always black-white? why are there never any asian-chinese or black-asian or chinese-black?