The Flirting Complex

I don't understand girls. Being a girl myself I really should understand us better, but as of yet I am still confuddled.
As always, I was on the bus when I made this revelation that I do not understand my own sex. I was people-watching (my favourite activity of all time) when I saw this rather cute boy who was encompassed by these two girls - one sitting next to him and the other sitting in the seat in front and leaning forward. Whenever the two girls talked to each other it was just like how any humans talk to each other - they smiled and chatted normally. Whenever the guy said anything they laughed. Not just any laughing - I'm talking throwing-head-backwards-laughing-like-a-loon laughing. This was usually accompanied my a "Oh, stop! You are bad!".
In particular the girl in front was flirting outrageously - leaning forward and touching the guys arm, doing her trilly little laugh and constantly patting/flipping her hair.
Here's where the mind boggles: if a girl likes a guy (like Flippy Hair obviously does here) then why doesn't she ask him out? It's like we're back in Pride and Prejudice days where the girls had to flirt and try really really hard for the guy to like her, in the hope that he would marry her.
I, personally, don't know of any girls who would ever ask out a guy. Personally? In theory I would but in reality...you know the Knight situation.
It's like we're afraid that asking him out means he's just not that into us - but when a guy asks you out then it's normal.
Hence the mind boggles.
It's not just this; flirting in general confuses me. I mean, don't you get tired of having a smile plastered on your face? Doesn't flipping your hair cause your neck to ache after a while? As you can tell I have never flirted with a guy in my life - I just act like he's a girl and talk to him like a human being not some sort of Sex God.
Maybe that's why I'm single...

Must dash, have to do some work! Procrastination/Twitter is the root of all evil...
Keep you posted,
Grammar Gal