According to Dr. Lilian Glass, an expert in body language and author of The Body Language Advantage, something as simple as the way a person sits can tell you a lot about who they are.
If you sit with good posture, both feet on the floor and your back straight ... You are confident and self-assured
If you cross your legs at the knee ... It is a sign that you are insecure.
If you sit cross-legged ... You are artistic, carefree and open-minded.
If you sit with your legs crossed at the ankles ... You are confident and secure.
If you choose to sit in the center of a couch or a bench ... You know what you want and aren’t afraid to get it.
If you sit with your hands clasped in your lap ... You are a people pleaser with a tendency to lie.
If you keep your hands still in your lap ... You're close-minded.
If you sit with your arms crossed ... You are unhappy and angry.
If you sit on your knees ... You’re an aggressive person.
If you splay your knees out to the side ... You are flirtatious.
If you lean back on your palms ... You are judgmental of others. (Redbook)