My rule of thumb on “macrogestures” (the big stuff, like arm and leg crossing) is to picture people nude to give you a quick assessment of body language. Body language cues came about over our primitive evolutionary history as the naked ape, so it naturally follows that they developed without clothing or coverings. Clothing provides a blanket to hide our genitals, or chest and breasts, our feet and so forth, but the hardwiring in our brain functions as if they are totally absent.
Imagine, for example, a full body steeple, sometimes called “hooding” where the arms are placed behind the head and the body leans back with the legs spread wide open – a crotch display! It is the way a proud (or arrogant) man sits to put his full package on display. True, it is slightly less offensive with clothing on, but it still carries the exact same meaning since its true intentions were delivered as if the clothing were absent.
Picturing people naked helps us to think about not just the message, but also the route behind the message. Men who hold their legs spread wide open are perceived as arrogant but women who hold the exact same posture will be thought of as sexually open or “easy.” While each party might not specifically intend to deliver this message, it matters little to how others subconsciously perceive them. Arm crossing is a protective gesture aimed at shielding the heart and lungs, and for women, the sexual breasts. What does it mean when we hide and protect these areas with our arms, how about a purse, a book, a podium? Shielding and negative emotions; lack of comfort!