Having one leg over the arm rest of a chair is a full on assault to the rest of his company. I use “his” because men are much more likely to use this posture than women. The posture shows aggression, dominance, ownership and an informal attitude. Ownership here can mean simply of the chair, but in a larger context it also means ownership of the situation as a whole, the ideas in the room, and even the people. The sitting position is so informal that it means that a person holding it, cares not about what anyone else thinks.
While, with friends this posture could be acceptable despite its offensiveness, it’s definitely not acceptable during an interview, in public, or when meeting important people. To send the proper message with our legs use a comfortable, yet proper sitting position which is a sign of respect for those around you. Either leave a slight gap between the legs, use the figure-four leg cross (for men only), or us the English style leg cross where the legs lie parallel one over the other. Women should almost universally cross their legs so they lie parallel, even if they are wearing pants but especially if they are not.