The phenomenon of becoming fascinated with a casual acquaintance or friend of a mutual friend to the point where your perception of their awesomeness inexplicably inspires you to initiate a new friendship. Upon meeting said new-person the afflicted are riddled with feelings similar to those of a real crush; such as wanting to spend time with them, laughing at their jokes more than others, admiration, girly giddiness, etc., Friend crushes are notorious for striking quickly and inciting gossip. Friend Crushes are more commonly observed in females but are also rampant in the male world, albeit manifesting themselves in slightly different ways, see male specific definition under Man Crush
When you really start to feel a strong connection with your best friend regardless of sexual orientation or gender. You feel like you always want to be with them. When you hangout, you want to be touchy-feely but it's not necessarily romantic. Just close. You get a bit jealous when they hangout with other people and you think about them all the time. It's like being in love with them without wanting to do them. Unless you do...then go you!
I've been feeling a best friend crush for Alice. I always want to hangout and cuddle with her.
When you have deep emotions for your "best" friend and you really really want it to stop because you told them and he/she doesn't see you in that way but they continue to talk to you and flirt in a way because they know. You hurt when you see them with other people but continue to cheer them on because you love them and want nothing but the best for them. You have so many mixed emotions about the entire situation and it just keeps getting more and more complicated. Maybe you should just tell them to stop leading you on. Yeah, they're your best friend, but that doesn't give them the right to play with your emotions just because they like the attention. Or maybe you should stop being clingy and paranoid. They'll be others. Wanna be just friends? Well fine. Tell them you're just friends, if they don't like it, that's them. They need to get their priorities straight.
Girl: who do you have a crush on?
Person: my best friend...
Girl: a best friend crush huh?
Person: yeah...it sucks but I can't stop it.