Phrase common in NYC, but useful in many metropolitan areas, particularly those that boast a top-tier law school. A "law school girlfriend" is a young lady with a non-descript corporate job (i.e., she works in "sales," "PR," or "marketing") and dates a man attending a nearby top-tier law school. She has no actual redeeming qualities, save being very attractive and urban chic. She uses her looks and her pseudo-corporate job to impress the law student into dating her, with the hope that he will marry her once he graduates and begins making $200K a year.
Law Student 1: Yo, you met Dave's new girl, right? What did you think?
Law Student 2: She's pretty hot, and works downtown or something.
Law Student 1: Law school girlfriend?
Law Student 2: Totally.
A hot girl between the ages of 20 and 30 who chews gum with a stupid, vacant look on her face and is somewhat promiscuous.
A girl need not be chewing gum to be labeled a gum chewer, but must look so stupid that one could imagine her chewing it in the manner described above.
That hot little bitty over there is such a gum chewer.