With thanks to the mighty commodorified, please to read synecdochic's excellent essay on How Not To Be That Guy.
It will explain, in painstaking detail, both why I tend to go ballistic on people who are a little pushy with their advice, and also why so many people were very very upset about the OSBP proposal. (If you don't know about that, here's the post I've seen that most successfully, for me, discusses same.)*
Money shot, as jaylake would say (And yes, I typed that in full consciousness of the irony thereof):
You are never going to eliminate all of the unconscious assumptions that your privilege -- whatever that privilege might be -- has programmed you with. You do not have to devote your entire life to crusading against sexism or racism or ableism any other kind of -ism there is. What makes you not That Guy is recognizing that you have that privilege, that your experience is not everyone's experience, and -- this is the critical part -- not assuming or behaving as though your perspective is the only perspective and anyone who doesn't match it is wrong.
Los Angeles Times piece on Men Who Explain Things, which explains (hah!) with case studies why exactly it is that sometimes this behavior comes across as condescending or unwelcome. If you are a Man Who Explains Things, go read it. It may produce healing.**
timjr with a very handy field guide for the geeky boy on How To Talk To Girls At
*(Now if somebody would only write a similar guide for people who would like to teach you how to care for your new piercing/new baby, life would be grand. Get the hell off my lawn!)
**NB: People who explain things in their own LJ/Blog/whatever, or when asked to explain them, are exempt from this categorization. Listening to actual experts talk about what they do is almost always interesting. Even if you don't know a damned thing about it. Having just recently spent hours reading BASE jumping boards and articles, trust me, even the impenetrable bits were interesting.