Although I do a lot of walking in the summer (5-6 miles a day in short segments) I also do a lot of sitting in lectures and programs. Sometimes it takes several blocks to get the kinks out when I start for home. So I finally decided I'll need to break a very bad habit--sitting with my right leg crossed over my left knee. Yes, as always, I researched it, and was horrified to read all the back, neck and leg problems that causes. That's why your hairdresser always (at least mine) tells you to uncross your legs when you're getting a hair cut. Really throws everything out of alignment. But breaking a habit of 60+ years is very hard. Now, I'm only 12 hours in to this new life style change--hope it helps. My FB friend Debbie says that she gave it up after years of pain, and it was like a miracle!
When seated with your feet flat on the floor and both buttocks in contact with the chair, the force of the position is applied naturally and equally to the lower body.
However, when sitting with the legs crossed, all the downward force is applied to only one side of the lower body, concentrated on one half of the buttocks, the sacroiliac joint and the hip socket. http://www.sciatica-pain.org/sciatica-from-crossing-legs.html
Cross-legged sitting resulted in a relative elongation of the piriformis muscle by 11%, compared to normal sitting and by 21% compared to the length of the piriformis when standing. It should be noted that the leg that was crossed over top of the other was resulted in the greatest elongation. The leg crossed over the top is in a position of
relative hip flexion, hip adduction, and hip external rotation. http://www.damienhowellpt.com/pdf/crossed%20legs.pdf