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n., a woman who has had sex with the same person you have. In the plural, vag sisters are two women who have had sex with the same man.

This is most likely unintentional. The two women may not be of equal merit physically or mentally; it may therefore be an unpleasant surprise.
Angelina Jolie and Jennifer Aniston are vag sisters.
by bajingo, bajingo, bajingo May 10, 2009