Kinda like one of my best friend's other best friends, but I feel it'd be weird for me to outright go for it. Plus I'm pretty sure she would never go for me.
Since we're sharing women stuff, eh?
If your best friend doesn't like their best friend in that way, go for it mate.
I'm not going to lie, I'm not attracted to the girl I went gym with. I have a laugh with her, but that's as far as it goes.