When in a large group of people you, under the cover of a blanket, put your hand on someone's leg, stomach, or other like places. Making sure that noone other than you and the recipient know what is going on under said blanket.
Last night I was at my girls place and we watched a movie with her parents. It was cool though we subtle cuddled the whole time....they had no idea.
When you're hanging out with a friend that you want to become more than a friend, and you employ various maneuvers to draw them into actual physical contact that can be construed as just "overly-friendly" or playful.
Examples include: laying your head on someone's shoulder when pretending tiredness; when there is limited seating, sitting on the floor in front of someone sitting on a couch and leaning back on their legs; back massages--a friendly gesture in any case, but with the intent being to get closer to the person.
Usually only used by kids
He got all of his girlfriends in high school using the old subtle cuddle.
When a guy yawns, and puts his arm around a girl. Usually in a sneaky or subtle way to feel her up.
Girl 1: Did you hear? John totally tried to feel me up!
Girl 2: Oh no! Did he use the subtle cuddle?