Back in the early 1950s, fumble parties became all the rage, according to Life magazine (July 14, 1952), which offered this description of them:
When everyone is disguised, they all fling themselves down into a huddle on the floor, making a confused tangle of bodies, arms, and legs. Then the lights are turned off. ‘It’ reenters the room and, by fumbling among the tangled bodies, tries to identify a person. If someone is identified, then he or she becomes ‘it’. But if the fumbler makes an error he must pay a penalty decided upon by the group.
So it was a bunch of adults feeling each other up in the dark. Sounds like a swinging good time!