Not everyone can physically cross their legs, either their legs are too short, too thick or both, GGs and GMs alike. I can't cross mine at the knee, and will never be able to. I'd like to be able to, but I'd also like to be taller and not suffer from male pattern baldness, but hey life is unfair sometimes. I can cross them at the ankle for a while, but it does get fatiguing, especially when wearing higher heels.
One tip for those who find it uncomfortable to keep your legs crossed at the ankles: If you are sitting at a table in a restaurant at a table with a tablecloth that hangs over the edges, you can put your legs under the tablecloth, relax your legs and sit however you like (since no one can see your legs or anything else.) This can release the strain of having to cross at the ankle so you can go back to crossing them at the ankle later on if you need to.
