Interesting, I've never heard anyone tell anyone else that sitting cross-legged is somehow unmanly. (I'm German). More like "don't sit like that in a professional setting" but that's also not something I remember anyone saying, it's more tribal knowledge.

Yes, it's pretty uncommon seeing people in public do it (sometimes on the floor or on ledges), but there are not many opportunities.

As a relatively big guy, I absolutely envy some of my smaller colleagues (yeah, mostly women) who can sit cross-legged in their office chairs - I'd absolutely do it, but I'm just too big, and just crossing one leg under the other often leads to numbness after a while.