Yeah, Dice. You're an alien species with incomprehensible emotions. Tell us.
Dice, you're a girl (most of the time)
I don't know how to approach this. I can KIND OF speak to her in casual conversation, as I asked her about her leaving to join the military, and the three of us (her, me, and my sister) were all bullshitting in general, but I can't say anything that matters to her, such as "I like you" or "You're beautiful" or even something as silly as "What kind of movies do you like?". I'm trying to be intelligent about why I can't just ask her out or something, but it defaults to a simple reason. Not shyness or self esteem...entirely. Hell even rejection isn't that horrifying.
Bullshitting is great, keep up with that, I'm sure a lot of relationships have started through just goofing around. Saying "I like you" and "your beautiful" though?? No. No, no, them words are off-limits until you know for FACT there is a spark. Saying that otherwise can send her for the hills or worse, make it too easy for her and she's out, she knows she has you hook, line, and sinker. Rejection happens, it's a fact. I've been rejected plenty. It happens, it hurts, you get up and -gracefully- move on.
What if she says yes to a date and I screw it up, or we just don't click, or something equally horrible? I can deal with being shut down, anger and rage are sort of bedfellows in my life. But embarassment, incompetence, worst of all the thought of blowing my only shot with her...it is making me feel queezy just typing it here. I know if I said hey, lets go see a movie when you come back, she'd say sure. But I desperately don't want it to fail, enough so that I'll let this feeling of desire linger til I'm more confident with myself and what I can offer as a guy.
Nothing will stop you more than being shy/timid/nervous etc. If there's a click, first date awkwardness won't even be a thang, likely she'd have it too, then you look passed it because you still had an "ok" time and wait for the second date where you're both that much less nervous but both agreed for a second date.
Boyfriend and I had a really awkward first date, barely said anything at all (seeing a movie together helped, you don't have to talk much aside from goofy commentary during it. Four years later, we're best buds, and talk about any/everything.
Also to, keep in mind it is your sister's BFFF. This might be awkward for your sister, not just for you. What's it like for your sister to welcome her friend into the house only for her to be seeing you instead? You gotta approach this gently, a day at a time, but remember -- if it was meant to happen, it will.