It was April 1971, Vietnam was full-on.
I was talking to a girlfriend who was trying to decide whether to stay with me or go back with her boyfriend who was about to return from Nam. I somewhere got tongue tied between Fuck and Naughty. Somewhere between thought process and sound "Nookie" popped out. She said, "What'd you just say?" We both laughed, I immediately started using the word at every opportunity. The month was April.