Maybe geography plays into things. Living in the south and having family living even further in the south, it's a stereotype I've run into often enough for it to be downright tiresome.
I think, though, the TV/movie stereotype plays into it more than anything else, especially with Latin. Even DWTS is not always helpful there with the costuming. (Ballet, I'm afraid, is a bit like skating, there's enough truth to the stereotype to make a lot of men uncomfortable.) And ronalds's sort of right, though flexibility specifically is more about genetics than gender, people just don't realize it...I've mentioned before, NP was much more flexible than his wife/partner, and is the only teacher I've had who asked if I've EVER been particularly flexible, even as a kid. (No. Never been able to do splits, stretch my back especially far, was terrible at gymnastics and tumbling even as a tiny kid.)