scalp sex
Whilst in the throes of passion (most easily done in the doggy style position), the giver pulls the receivers hair as tight as possible. Once the hair is taut, the giver brandishes a tomahawk and proceeds to scalp the receiver. Once the scalp is removed the giver proceeds to climax in the receivers open scalp wound.
Keith was terrified the cops would arrest him after he had particularly bloody "scalp sex" with his partner Tony the previous night.