Most Helpful Guy
Because the feminist crowd has a reputation for being surly ball busters.2
Most Helpful Girl
Your actions speak louder than words. Being a "feminist" these days is such a negative thing to declare, even if you are simply a woman who loves men and just wants to preserve the rights of women.
There are a lot of things you don't need to discuss immediately about yourself in the first few stages of dating that have tendencies to be offputting to many men. To a lot of men, saying you're a feminist is up there with other things they don't really need to know such as telling them you like being peed on, saying that you were gang-raped in college. If it just doesn't need to be said, don't say it. A guy will figure out first if he likes you enough and will get to know the things that are near and dear to your heart as far as what you advocate for. Once he gets to know the sweet and wonderful you, if you eventually tell him that it means a lot to attend a yearly women's group that petitions women's rights in Afghanistan, then fine. He will find out soon enough that you are all about equality without having to put fear in to him that you are against men.
For example, when I was dating, I put my atheism on the back-burner. I didn't want to reveal something that sounded negative if someone didn't understand what it was. Eventually the guy got to like me and then learned "oh she doesn't believe in god" but by then it didn't really matter, and then I could simply explain my views so it wasn't so in-your-face, something they needed to know about me immediately. It gives the impression that all other things don't mean as much to you. A guy wants to be the focus when you meet him, so to talk about him and ask him questions and be friendly with him will eventually make him see that being feminist doesn't define who you are as a person, but it is just a part of what's important to you as far as what issues mean most to you.6