A blowjob a man gets from his female patner when menstruation prevents the couple from having vaginal sex. Uncle BJ is often a man's only available option for sex from his wife or girlfriend when Aunt Flo comes to visit.
Wife: "You'd better forget about tonight, honey. Aunt Flo's coming for a visit."

Husband: "Well, I hope she brought Uncle BJ with her!"
by trxstr January 01, 2010
Top Definition
A suitable alternative for sex while your girlfriend/wife is menstruating also known as a blow job. More specifically as a counter to a woman who uses her period (Aunt Flo)as an excuse to avoid sex.
"I don't care if Aunt Flo is in town as long as she brought Uncle B.J."
by Saltine Nachos February 20, 2009
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