The intermingling of the sexes (males blue with females pink makes purple) in one of the following activities, depending on context:
1. innocent conversation
2. sex
The mixing of boys and girls, such as when on a school or churchtrip with regards to rooms, talks, etc.
On our school band trip, the teacher told us not to go into the room of the opposite sex, but we were still purpling anyway, because they didn't care, and they we our friends.