Somewhere through the years, things got complicated.
Seemingly "over night" they became more concerned with the little things, which in turn led to invitations to said dances containing specifications like, "ladies are encouraged to wear dresses," "please wear modest formal wear," and, "men wear long sleeve button shirts with dress pants. No jeans."
"Encouraged," because there is nothing they can do if you don't, but something is wrong if you wear anything but? "Dresses," because women shouldn't wear pants? "Modest," because we don't know how to dress that way without being told? "Dress pants," because jeans are, what, unorthodox?
My question is, when did what we wear become more important than what we say, think, and do?
Putting too much emphasis on the physical, on what's outside our bodies, is no better than what the Pharisees did. They were so concerned with what others thought and perceived of them that they neglected what was really important - the heart condition.
"34 Brood of vipers! How can you, being evil, speak good things? For out of the abundance of the heart the mouth speaks. 35 A good man out of the good treasure of his heartbrings forth good things, and an evil man out of the evil treasure brings forth evil things. 36 But I say to you that for every idle word men may speak, they will give account of it in the day of judgment. 37 For by your words you will be justified, and by your words you will be condemned.” Matthew 12
If our hearts are captive to The Lord, we don't have to concern ourselves with all the little details like dress, pants, or modesty. Because if our hearts are captive to Jesus, we seek to do what is pleasing to Him.
And the rest of it is just minor detail.
I know families have different ideas about modesty, but if we seek to honor God and concern ourselves more with causing him offense then each other, then it won't be as big of a stumbling block when we see other Christians wearing something we personally wouldn't wear for modesty's sake.