The feminist blogosphere is once again discussing
the perennial question "can you be feminine and feminist?" The central question is framed as whether certain preferences, such as shaving, are endogenous or imposed by the patriarchy -- with the assumed corrollary that the former are acceptable and the latter should be rejected, even if the behavior they cultivate is the same.
But I think the origins question is not the most important thing (which is not to say it's not useful to examine). On the one hand, the dichotomy between "real" endogneous preferences and external imposed ones is false -- all of our preferences are the result of an interaction between internal states and our environment. More importantly, the advisability of satisfying, thwarting, or changing a preference is not a function of the preference's origin. More important than their origins are your preferences' structure and consequences.
Structure-wise, we can divide preferences into base-level and instrumental. Base-level preferences are those that we want for their own sake. Mostly this will be general things, like security or recognition or happiness or leisure. Instrumental preferences are things we want because they contribute to base-level satisfaction (or to another instrumental preference which contributes to a base-level one, etc.) -- so, for example, I want lots of people to read and link to this post because that contributes to my desire for recognition. Base-level preferences are not necessarily endogenous -- a socially-constructed preference can easily become lodged so deep in our minds that it's felt just as strongly, and as genuinely, as any other preference. And it therefore has the same moral status. Note also that (presumably due to a psychological mechanism for reducing the brain's workload) instrumental preferences masquerade, in day-to-day life, as base-level preferences.
When we ask "why do I want X," the most useful answer is in terms of the logical structure of our preferences. In this way we can clarify whether the things we want on the surface are really the most efficient way of satisfying our base-level desires. One key mechanism used by patriarchy (or any other social system) is to convince us that certain things contribute to base-level preferences even when they don't. Such mistaken preferences -- whether imposed by patriarchy or our own innocent ignorance -- can then be thwarted or unlearned.
However, that's not patriarchy's only mechanism. Patriarchy can set up our environment -- the structure of the options available to us -- so that certain behaviors truly do contribute most efficiently to our base-level preferences. The key question then becomes what the effects of satisfying, thwarting, or unlearning that preference are on all concerned. Say (to jump into another domain) I have a preference for having veal parmesan for lunch. What matters is not whether I prefer veal because my tastebud genes are such that veal is very tasty, or because given our culture it makes me feel sophisticated to eat the fanciest dish on the menu*. What matters is the consequences of my actions -- my own pleasure, the suffering of the calves and slaughterhouse workers, etc. Depending on how those consequences stack up**, it may be that I ought to order eggplant parmesan instead.
So can a feminist be feminine (or a male (pro)feminist be masculine)? I can't issue a blanket statement. But the answer in specific cases is to be found by asking whether the behavior in question advances your base-level goals, and feminism's goals, more than thwarting your desire to do it.
* Assume for the sake of argument that my actions in either case are identical, though of course in practice it's quite plausible that they would differ in detail. What's important is the actual, rather than the intended, content of the actions.
** I'm presenting the issue in simple utilitarian terms, but the point holds if the consequences at issue include rights violations, and if certain consequences are a priori ruled morally insignificant.