Over coffee,

I think asking her any other way would be a bit creepy, say over the internet.
It would be creepy even over coffee.
“I’ve been looking at you like this for a while now…”
“And…”
“And I’ve been wondering.”
“What have you been wondering about?”
“If you’re available.”
“Drop it, chev. Every single girl in this town knows… yadda yadda.”
Or, worse:
“What if I am?” (Wiggles and twirls a curl. Upon which you should run for dear life.)
If she says yes, then take it easy. Have a nice time without any pressure. Definitely don’t start asking questions which make you look like you are desperate to propose marriage, if you catch my drift. That will make you seem creepy, and scare her off.
Plus, if a girl’s not a keeper as a friend, she’s not a keep as a girlfriend. (Minor exception when she claims to be a friend while acting as a girlfriend, which is sort of okay when she does actually want to be your girlfriend but not when she actually really wants to remain just friends permanently.)
We used to call this the Cindy Crawford syndrome. Guys that waited and waited for the perfect lady to come along while all their friends were out having fun dating normal women. : )
It’s even more fun when the person who didn’t date all sorts of vaguely not bad people like others did actually does achieve the dream and find someone special.

(Not talking about super model look really, though.)
Just ask her on a date. What do you have to lose? Do you really think that constitutes “girlfriend stealing?” If she’s not married, she’s free to go out with whomever she wants. If my husband had let my boyfriend at the time intimidate him, we might not be happily married today! Stop over-thinking this.
Well, if I had a so called girlfriend (“boy” and “girl” doesn’t sound right for adults), I would be pleased if she went on dates with guys. She could do that of course, but without continuing to be my girlfriend. And I’d probably not be interested in further participation in any capacity anyway barring someone who honestly admitted taking a step too far and asked to take it back, maybe.
Just wanted to say, this does not make you a coward. It makes you quite honorable. Generally (but not in all cases), it is the charitable thing to not steal another man’s girl. I commend you on that.
+1. Besides, don’t destroy something which is working.
Guys with iffy social skills can date and marry (it happens all the time), but it helps to be sweet, fun, a good listener, reasonably neat and hygienic, and professionally successful.
Actually, those are the qualities which make a woman think you’d be great in her friend zone.
Agree 1000% You can’t “steal” a girlfriend, as she is not property and has made no vows. May the best man win!
I take a different perspective—may the woman make her choice. I suppose your perspective is female-centric, while mine is a little in the opposite direction.
Now as for “no vows”, sure, a promise is not a vow, but I wouldn’t marry a woman whom I couldn’t trust with a blank cheque or with Brad Pitt in a dark locked room (or a gun etc.). I’d be understanding if she wanted to make sure (though I’d rather be told that openly), not close herself to meeting someone better etc., that’s all right if I’m afforded the same rights as she claims for herself in this regard (and I’m a bit skeptical as to how you would feel if the tables turned in your example, to be honest, that is if a man did the, “may the best girl win,” kind of thing), but if she actually broke a promise, even an implied one, the prospect would probably be dead even if she decided she were more interested in me than in the other guy. Friends don’t do such things to friends and I wouldn’t cast my lot with a woman who were not a friend I could depend on.