Three feet on the floor

A quote from David Gelernter, America-Lite: How Imperial Academia Dismantled Our Culture (and Ushered In the Obamacrats)

“Before the cultural revolution, there were no coed college dormitories with young men and women living in bedrooms on the same flour. Before the cultural revolution, visiting between men and women students on campus was regulated by ‘parietals,’ which limited male visiting in female dormitories to certain times, and usually required girls to return to their dormitories to certain by set hours and to sign out before leaving for the evening, listing their destinations or plans. When men visited women in their rooms or vice versa, the ‘three on the floor’ rule came into play: the door must always be open and there must be three feet on the floor the whole time.”

A quick search in Internet:

the infamous “three feet on the floor” rule, which required that, when a boy was in your room, the door had to be open and three feet had to be on the floor at all times, hence preventing any romance from progressing irredeemably far