Free-bleeding is the practice of abstaining from using sanitary products during one’s period.
In 2014, the infamous imageboard website, 4Chan (which is basically Reddit for awful people*) thought it would be a funny hoax to pretend free bleeding is something radical feminists do to protest sanitary products and the patriarchy.
As is so often the case with ignorant misogynists, the “joke” turned out to be on them.