1. Define feminism as the ideology that woman and men should have equal rights and opportunities. People might try to stick other stuff in there. Don't let them. Tell them, politely but firmly, to go get their own ideology or sub-ideology. And maybe a sandwich. They seem crabby, maybe they are hungry.
2. Tell yourself that you are equal to any man or woman in your universe. (And really beyond; not that we know how they establish gender in other universes. They might not have gender. Which would be interesting, just on a bathroom level alone, but if Ally McBeal's law firm could have unisex bathrooms, I imagine genderless alien races could figure it out, but what is really important here is that you are equal to all of them because you are amazing and beautiful and wonderful.)
3. Eat a sandwich. All that ideology and positive self-talk makes one hungry. You can eat with the crabby people, if they have calmed down.
4. You are full; of positive feelings and sandwich. This is great! Now go about behaving as if you are equal to any man or woman in your universe, and that any man or woman in your universe is equal to you. Do this as seems good to you; lean in, recline, do extreme yoga moves, lie on the couch and binge-watch House Hunters, be a great chef, order take-out, dress-up, dress-down, don't dress, have children, don't have children, act like children, attach, detach. The options are literally endless. Just make sure that you are being you; not an archetype or an example or a symbol. You are none of those things because you are so much more. You are a fully formed and flawed human being who should glory in the uniqueness of you, not try to hide it because someone you encounter tries to tell you that you are not equal to him/her. They just haven't done the 4 steps yet. Pity them and keep on being a feminist. Or, better yet, tell them about the four steps so that there can be more fully formed feminists to hang with; win-win! You might wanna start with #3. Never underestimate the power of a good sandwich. And never underestimate you. You are glorious.
Celebrate! You are now a feminist!
Make your celebration as unique as you are!
Even if that means a sock full of marbles.