The act of having his and her danger zones touch one another in a highly sexual erotic manner.
i.e: do the dirty, jump one anothers bones, sexing one up, intercourse, sandwich dancing, arousing with genitals, sexual friction, ect.
The other night, Harriot and I were bumping dirties real nice, when mother and father walked in. Family dinner will never be the same.
It was a dark cold night, the heat went out, and to keep things hot, mother and father decided to bump dirties. Nine months later came the consequence, ME.