Women who have had sex with the same man or men. The more men whom they have each had sex with, the closer the bajingo bond. The male version of this is called the weiner cuz. Note that bajingo sisters that have participated in threesomes or moresomes are especially close. Acknowledgement of bajingo sisterhood is often preceded by some degree of jealousy in one or more parties.
As seen on the TV show Scrubs.
Kim: Elliot, you're sleeping with my ex-boyfriend!
Elliot: Well, same goes for you!
Elliot: Yup. We're bajingo sisters.
*they make out* <-- Note: this may or may not occur.
Two girls that have had sex with the same man.
-I just had sex with J.D.
-Really? I had sex with him last week! We're totally bajingo sisters!