My High School health/gym teacher used to tell us - when you have sex with someone, just remember you are having sex with everyone they also had sex with.
Now days, make that "every one, and every THING they ever had sex with.
Veggies, animals, shared "toys", inflatable dolls, Liberals....
We had a poster by the entrance of the girls’ locker room in high school that illustrated that point. Looked somewhat like a family tree, but inverted... I very clearly remember that poster, and my health teachers mentioning that several times.