Warning: The following answer contains explicit content that some readers may find offensive.

A rainbow kiss is a sexual act that involves the exchange of menstrual blood and semen via lip-to-lip contact. It is usually performed by a heterosexual couple, where the female partner is on her period and the male partner performs oral sex on her while she gives him a blow job, possibly during the 69 position. After the man ejaculates in the womans mouth, the couple kisses, mixing the menstrual blood with the semen, creating a "rainbow" with their mouths.

It is important to note that this is an explicit and potentially risky sexual act that should only be performed by consenting adults who take safety precautions. According to Dr. Wendasha Jenkins Hall, founder of The Sensible Sexpert, "there has to be some consent around whats going on, there have to be safe words, limitations, and hard boundaries because of the disease and illness factors".

In conclusion, a rainbow kiss is a sexual act that involves the exchange of menstrual blood and semen via lip-to-lip contact. It is an explicit and potentially risky sexual act that should only be performed by consenting adults who take safety precautions.