After anal intercourse between either two men, or a male and female, the individual who contains the expelled seminal fluids uses the lavatory; defecates in the toliet, which produces feces mixed with semen. The defecator then proceeds to grab the feces out of the toliet and makes his/her partner ingest it.
Graham crackers are of course optional
1. Billy went to the grocery store yesterday to pick up graham crackers so his girlfriend could make a dirty s'more.
2. After intercourse, John turned to his friend Tony and said "That was the best dirty s'more I have ever tasted"
3. The dirty s'more has become undoubtedly the new "San Francisco Treat"