I'm going to flirt with my best friends crush
Why would you do that to your best friend?
Because it's just too easy to get into that girl's pants.
Even though your friend is not dating that person, it is not good to try to sleep with them. It will hurt your best friend and it would ruined your friendship.
I don't care. I want revenge on my friend for something that has nothing to do with her.
You are trying to mess up your friend's relationship. That is wrong and you should reconsider.