I find the friendzone is a feeling you get more than anything else - You like someone and they talk about being friends to let you down or avoid awkwardness. If there is any one sided attraction I don't think friendship can work , it just means one person has false hope.
When the girl treats you too friendly, like how she would treat her other girl friends. When a girl talks to you as a girl and is too friendly then you just know you fucked up lol. I by the way beleivr guys themselves put themselves in the friend zone. If they had the balls to ask her out then it wouldn't happen. And if they asked her out and she said no, then break off with her since trying to be friends with someone you like will just not work.
If you're in the friendzone you might still fuck her at some point, if you're in a really bad place with her she's not talking to you and doesn't know you exist. No such thing as platonic between the sexes.