As we all know, "the friend zone" has always been a great subject for comic relief. Many a comedian or television show use this term as a funny way of portraying how sad it is when men try to impress women, or women try to impress men, but the other doesn't reciprocate. Hilarious.
The truth is, however, not so funny. This invented "space" in which a man or woman is put when their person of interest doesn't live up to their expectations, is an offending and misplaced way to deal with a blown off ego.
Self-proclaimed "nice people"
A brief act of helpfulness, a compliment or a couple of kind words are quickly mistaken for a sign of attraction, but it works the other way around too: don't misuse kindness as means to an end. Being kind to another human being does not entitle you to a sexual interest from that human being. Being in love with someone does not mean that this person is going to love you back. And when this person lets you know that they don't feel about you the way you feel about them, you don't have the right to insult them or complain about how they put you in "the zone."
Consider this: maybe this person does, actually, see you as a good friend. And maybe, just maybe, throwing the zone in his or her face is just plain rude, and totally messes up this person, who thought of you as a friend. If you really care, you respect their choice, and are considerate of their feelings. If you can only be kind when you believe there's an opportunity for a relationship or even sex, you are not a nice person.
If you feel the constant need to define yourself as "such a nice person", maybe your actions should live up to your statements.
If you feel the constant need to put pressure on the fact that "women only date assholes", or "men don't want real women anymore", followed by a statement that proves you are obviously a much better catch, maybe the problem is not that you are a nice person, but the problem is that you aren't.
How is this related to feminism?
Well, the main concern of feminism throughout history has been fighting for women's rights, for them to have equal rights as men. Today, feminism still stands for those equal rights, for both men and women.
"Friend zone" is attacking women and men for their right to say "no."
"Slut" is attacking women* for their right to say "yes."
*The friend zone is used by both men and women, but women who have an active sex life are much more often called on it than men.
The big conclusion here is that the friend zone does, in fact, not exist. It is made up. Using it as an insult is a very immature way to deal with an unanswered desire, and could do much more damage than you may initally think.