Yesterday i was being C&F with this girl who ive known for a while but dont really talk to. anyway, i negged her and she gave me the finger, there was a silence for about 5 seconds, cause i didnt know what to say (she looked serious). then she smiled and everything seemed normal. it seemed i went almost too far and she was deciding whether or not she was mad at me but i didnt want to say anything in case she was really pissed off/about to be.
any thoughts?

You could turn that two ways. Either you drop it and do so in style...

...Or you go on about it. If she's seriously hurt it might be time to tell her it's a joke, but still be a bit cocky about it. Sure, there's a risk she'll think you're an asshole, but it's important that you don't lose your high value.

Ever heard that you should treat them like your "bratty little sister"? Go for it.

"Whoa now! Where's your funny-bone?"

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Another thing I can think of is to take the finger as a joke and seem overly upset about it, gasping, pouting and whatever.

"How could you!? Beneath this shell of awesomeness and pure bad-ass, I'm a really sensitive guy you know!"

...These are my two cents, at least.