Acting or even dressing 'like a lady' is a construct that runs deep. But come to think of it, there is something inherently flawed in the term. It suggests that which is suitable to and expected of a lady, i.e. delicacy and decorum. But as the role of women in society has evolved, so too has our understanding of what or even how a woman should be, act and even dress. As a result, the paradigm for the term ladylike must shift from what is appropriate (as prescribed by men) to what befits women in all their diversity and complexity.
Being polite, graceful and respectable are qualities that should not be expected by virtue of gender. Removed from the traditional norms of propriety and femininity, conducting oneself like a lady strikes me as being fiercely strong not lacking in strength or virility; elegant not fastidious and above all, true to self. So whether you are a tomboy or a girls girl, a jeans and tee girl or a pleats and frills girl, own it. And if like me you don't quite fit in this binary, then go ahead and mix it up - prim pleats and tough leather never looked so good.