Exactly. James Dean looks relaxed, important, intriguing, brooding, and mysterious. However, "hands in pockets" is only one body language cue. Pair hands in pockets with a proud chest, weight distributed on the back leg, and you've got cosmic fabulosity. He's not open, but he gives off a certain vibe.
Pair hands in pockets with hunched shoulders, sinking chest, evenly distributed weight... and you've got insecurity and low spirits.
I point to these purist examples of body languages and their behavior from
http://www.deltabravo.net/custody/body.php
NONVERBAL BEHAVIOR INTERPRETATION
Brisk, erect walk ----- Confidence
Standing with hands on hips ----- Readiness, aggression
Sitting with legs crossed, foot kicking slightly ----- Boredom
Sitting, legs apart ----- Open, relaxed
Arms crossed on chest ----- Defensiveness
Walking with hands in pockets, shoulders hunched----- Dejection
Hand to cheek----- Evaluation, thinking
Touching, slightly rubbing nose----- Rejection, doubt, lying
Rubbing the eye----- Doubt, disbelief
Hands clasped behind back----- Anger, frustration, apprehension
Locked ankles ----- Apprehension
Head resting in hand, eyes downcast----- Boredom
Rubbing hands----- Anticipation
Sitting with hands clasped behind head, legs crossed----- Confidence, superiority
Open palm----- Sincerity, openness, innocence
Pinching bridge of nose, eyes closed----- Negative evaluation
Tapping or drumming fingers----- Impatience
Steepling fingers----- Authoritative
Patting/fondling hair----- Lack of self-confidence; insecurity
Tilted head ----- Interest
Stroking chin ----- Trying to make a decision
Looking down, face turned away----- Disbelief
Biting nails----- Insecurity, nervousness
Pulling or tugging at ear----- Indecision
Know what pairing and playing with body language makes YOU portray.