Did you hear about the female rapper who only rapped when she was on her period?

This joke relies on a play on words involving the term “flow,” which has multiple meanings in different contexts. In the realm of hip-hop and rap music, “flow” refers to the rhythm and rhyme style of a rapper, particularly how smoothly they deliver their lyrics over a beat. A “mean flow” in this context would suggest that the rapper is exceptionally skilled or has a very impressive style.
Simultaneously, the term “flow” is colloquially used to refer to a woman’s menstrual period, where it describes the physical process of menstruation. The joke combines these two meanings: it describes a female rapper who raps only during her menstrual cycle and suggests that her performance is particularly powerful or aggressive (“mean”) during this time.