>>2 has a valid point. Why else would they move to cover their chest? Because your presence makes their boobs cold?

Seriously, they say that the first 10 seconds in meeting someone is the most important for making an impression. And for your information, it takes less than 3-5 seconds for a girl to notice that you're looking at her chest. A split second glance would be enough to reach for the jacket. You're obviously doing something wrong within those 3-5 seconds, which is something either body language or appearance related.