what is a rainbow kiss - A "rainbow kiss" is a term from sexual slang that refers to a specific and controversial intimate act. It typically involves a partner who is menstruating and another who has recently performed oral sex. The act is described as one where menstrual blood and semen mix during oral activity, and the participants then kiss, sharing the combined fluids. The name "rainbow kiss" is derived from the mix of red  and white , though the term is more figurative than literal.