Tell-Tale Skid Mark

After engaging in the act popularly referred to as "69" with his girlfriend, Brian remembered he had an appointment with the dentist. He was afraid the dentist would notice the smell of fanny on his breath so he brushed his teeth, used dental floss, and, on top of that, a bottle of mouthwash. As he arrived at the dentist's office, he ate a pack of strong mints. His turn came, and the dentist told him to take a seat. Feeling confident and relaxed, he opened his mouth wide. The dentist got close and said, "Did you have a 69 before you came here?" Brian answered, "How did you know that? Does my breath smell like fanny?" The dentist replied, "No, you have a skid mark on your forehead." Merrily