When you are laying down on your side and someone sneaks up on you for a spoon thus initiating the sneaky spoon.
Usually the sneaker will be the big spoon but not always. Depending on your sneaky skill level, you may be able to pull off a little spoon - sneaky spoon.
It is common courtesy to whisper the term "sneaky spoon" into the person's ear once in position.
"Oh they're laying down...time for a sneaky spoon..."