one who once practiced promiscuous sex, but has since dedicated her/himself to long-term conservative relationships. In America reformed sluts usually engage in promiscuous sex during the ages of 18-23, since these are also prime years for developing life long interests, reformed sluts will hardly have developed skills for any non-academic interests: cooking, dedication to engaging in sports, general taste in music, cleaning, outdoorsmanship, bilingualism, etc. This is usually referred to as bimboism.
Likewise if one finds the above qualities in a guy/girl, then it is unlikely he/she is a reformed slut.
Gene: ...but I heard Mark's girlfriend can't cook.
Paul: Of course she can't cook she's a reformed slut.
Gene: So all she can go is talk insistantly and give head?
Greg: Hey I asked my girlfriend how she felt about sex.
Greg: She said when she feels she's reached that point in the relationship she considers herself ready.
Pete: She didn't say how people she's been with?
Greg: Uh...no...I really didn't ask...
Pete: Bruh, that's a reformed slut answer, RUN!