This isn't really suppose to happen, but occassionally it does.
Some of these girls wear the hijab becuase of their families or because of where they work. But when they are in the open they take it off for one reason or another. I knew a couple of girls like that at high school. Now before someone goes on a rant saying these girls don't want to wear it at all and are being forced to do something they don't want to, it should be noted that most of these girls acutally took it off because they didn't want to be teased. Of course there are those who just don't want to wear it, but surprisingly those girl eventually put it on later in life because they want to.
The girl that probably touched you in the store was either playing you, or is more of a wild girl than you'd think. There was one girl in particular that I went to school with that wore the hijab, but would give select guys BJs. Even though they wear hijabs they are still women are are tempted by the pleasures of the flesh.