This is an abbreviation for the term "Dirty Little Girl". This term is used when referring to girls that are dirty and little while in their presence leaving them incapable of knowing or responding to said insulting terminology. You are a dirty little girl, when you are both slutty, good looking, and of small proportions.
Man A: She is such DLG, I would totally R and M that. (R and M stands for Rape and Murder)
Slut A: Whats that?
Man B: Don't worry about it, nothing.