After having intercourse with a female who is menstruating, you then proceed to have anal intercourse. After that is finished, the female may flatulance, resulting in a fine red mist, or a "blood fart."
"Joe was doing this chick in the butt after he fucked her in the puss when she was pms'in it. So she had a blood fart!
by Nathan the freak February 19, 2007