Outdoor Intercourse Day began at least by 1969 at WSU. That year was my Freshman year at WSU. The Editor of the University paper was fired for publishing a picture of four feet behind a log, two pointing up and two pointing down. One pair of feet were male and the other were female. The article was celebrating Outdoor Intercourse Day, May 8th or the 69th day of March.
Small town in Lancaster County PA. Home of the oldest Amish settlement in the country. It's part of the crazy town names in the area. Just down the road is Bird-in-Hand, across the field is Paradise, and over the mountain is Blue Ball.
To get to Intercourse, PA go through Bird-in-Hand, pass Blue Ball, stay on the same road, and you'll find Intercouse. Afterwards you'll go through Paradise.
An alternative phrase for 'fuck buddy'. May be more widely used when in the presence of a more adult, or mature crowd. Also works in front of cops to lighten the mood when making a report.