Mechanical differences between male and female skeletons: Clavicles, Shoulders and Arms

Men's shoulders are straight, their clavicles are thick, straight and long.
Their arms are more muscular and straight. They hang straight, because men's hip are narrower than their shoulders. There are no hips to avoid contact with. 
Men have longer arms compared to their body size than females.

Example of long, straight male arms: Charlene of Monaco

Women's shoulders are sloping, their clavicles are thin, V-shaped and shorter thans men's.
Their arms are not straight, but angle outward  from the elbow. This is called the "carrying angle" and is seen when the arm is extended straight by the side. 

Female arms hang akimbo to avoid contact with their hips, when walking. Female Skeletons move their hips and swing their arms when walking.

Female arms are more soft, less muscular. Female arms bend a little further from the body and are more flexible at both joints, due to the laxity of female's thinner and softer ligaments.

A male (left) and a female (right) skeleton walking, holding an umbrella. Watch how each one holds its arm. Watch the different angle of the upper arm in relation to the torso & where the top of the umbrellas are pointing.

Male arms are straight, hanging straight, whereas female arms are not straight and hang akimbo. 

Training - see more examples of shoulders, clavicles and arms here !