In the grand scheme of things in this world, I like to think I am reasonably laid back. I am perfectly happy to hold my opinions to myself when people's choices and actions are out of line with what I think are right, so long as they are not causing harm to one another. But the one area where I refuse to sit back is when it comes to others telling someone about their experiences. Here's the thing: We all have our experiences and our ideas, and what we think about the world comes from those things. Some people have had really comfortable, easy experiences, and some have not. Some people have had experiences that align with the first impression you might get of them, and some have not.
If you want to get under my skin, tell someone about who they are, for them. Don't let them speak for themselves, or (oh forbid!) ask them about their experiences. Please, pigeonhole them and make assumptions -- especially if this is something you get upset with others for doing to you. This is ideal.
Because above all, feminism is about telling others about their experiences so that you can be right and unchallenged.
OH WAIT. It isn't. At the end of the day, the one thing we can do for one another, that will help this world be a better place, is to listen. We can listen to what people have to say, and ask questions. We can let them ask questions of us, and share their experience. Assumptions will get you nowhere. So please, for the love of pineapples and red wine, practice what you preach. Listen. Ask questions. And don't assume you know someone or where they come from. Remember that what someone looks like doesn't guarantee the past they have grown up with, or the family they come from.