Or you can add the words "between the sheets" to fortune cookie fortunes too.
We did the same thing, but we added "in bed" to anything, anyone said. It made for many instances where an adult was speaking and, out of the blue, two teens would look at each other and practically die, laughing, over something that was not the least bit funny.
Once an older teacher passed away, over the weekend, and when our vice principal announced it to the assembled student body, he mentioned that she had died "in bed". I could not hold it in. I guffawed at the death of a teacher. I explained it as a nervous laugh, but all my friends knew that I had lost it, completely.