Breeder is a slang term used by homosexuals to describe heterosexuals; this term may be used in a joking or derogatory manner. It is drawn from the fact that homosexual sex cannot lead to reproduction, while heterosexual sex can. The reproductive aspect of heterosexual sex is implicitly being mocked by the pejorative use of "breeder", which connotes the topic of animal husbandry.
Breeder can also be used as a derogative term for people who have children especially those for whom the children are now the centre of all their attentions, the parents often drifting away from previous friends and lifestyle.
Furthermore, another definition of Breeder comes from the BDSM community in which a breeder refers to a human female who is forced to have children and thus breed.