Oddly, I see this question come up quite frequently. My initial gut reaction is: who cares? I would say that if a man wants to be supportive of a particular cause, why suggest that he cannot? I'm not stricken with cancer, nor has any member of my family ever been, but I don't think the American Cancer Society would turn down my offer of support in helping fight the issue because of this reason. Perhaps feminism is distinct in a way that I'm failing to identify.

Naturally, there is the risk that a man calling himself a feminist might do so for the wrong reasons, or he might misrepresent the movement itself. Many men tend to be sexist inadvertently, in ways of which they are not aware. A squadron of men running around with shirts reading "This is what a feminist looks like" while perpetuating rape culture could do more harm than good in their community. Making a movement completely inclusive allows it to spread to more people, but the median amount of passion and understanding of the core mission will most likely decrease.

Perhaps most importantly, if you use the measure of how much a person "gets it" in order to determine how worthy they are of being a card-carrying feminist, there are certainly women who call themselves feminists who would fail the litmus test as well. (Whatever such a test might entail.)

It's not a terrible question to ask if there should be a standard to which all feminists should hold themselves. Like any cause for social justice, I'd believe this is something you should commit to over time, not only in word, but in deed. It shouldn't be enough to apply the label to yourself one day, then simply coast on whatever knowledge brought you to apply the label. Culture changes, as does the body of knowledge with which one must be familiar to understand the mechanics of oppression.

This is especially true, I believe, if you are a man. Women live the understanding of their oppression in our society every day...though they may not be automatically or intuitively aware of how they should modify their actions in order to effect social change. As men we must continually seek this understanding, make an ongoing effort to scrutinize our own actions, and change them to not only avoid doing harm, but in an effort to do good.