What would you do if a person you considered a friend turned out to not like you at all?

Ah if revenge was tasty like in the movies... They are no different than any other toxic person, remove them from your life as much as possible. Don't even waste the energy with them fighting about justifying it, they are likely wanting to watch your anger as amusement. Don't be their victim just move on with your life and find your own happiness and better friends. People who hurt and manipulate others for fun always get their due eventually. You reap what you sow.

+1 on Schneider. You notice someone is not liking you at all, you can let that person disappear. You can speak fewer, you can dodge the person, or you move on your "people" focus to others.

Happened plenty of times in my childhood. :/ You just gotta face it and look for real friends, forget about the people who don't care about you at all.

I've had this happen once in my life. At the time it was traumatic and he just suddenly turned into a douchebag out of literally NOWHERE. Got in a dumbass fistfight and never heard from him since my Junior year of highschool. lol. Good times.

I've had this happen before. I just stop contacting them and let them do their own thing. I can't change other people. Some friendships are temporary because other people change and end up doing different things. If they don't want to talk, then fine.