I do this too! I'll get up with a dead foot and think "I should really not sit like that again"...and then I sit back down and do the exact same thing.
I also cross my big toe on each foot over the next toe very often while I'm laying down or sat down with my legs up on the recliner. Again, I don't realise I'm doing it and then if I do notice, I stop..but it usually happens again.
Yeah, I don't think I do it as often as I used to when I was younger either. My shoes are always worn down on the outside more than the inside because I think I walk funny but yeah, standing on the outside edge doesn't help!
My son, always sleeps (from he was a toddler) with his legs crossed underneath him facing down... i used to worry and place in on his back - but in the morning he'd always be back in that position, i used to ask him if it was uncomfortable or was worried he'd damage his knees etc... but he always said that it was the most comfortable way to sleep for him...