Okay. I'm game if you are.

We talked and sipped at our straws,
With some friends you haven't seen much of, it sometimes takes a bit to get the awkwardness out of the way and get back on track.
I hadn't really even said ten words to her in months, only "Hi" now and then in passing.
We sat like that for quite awhile, maybe an hour, maybe more. Who knows? Time didn't mean a thing on such a sleepy summer's day.
Don't sell yourself short, Jimbo.
I want to send something to shake that boy up."
For the first time, too, I noticed I was now taller than she was, quite a revelation.
"Then what if we take those last two au natural?" She locked those jade eyes on mine. "You know, go for broke. All the way. I'm game if you are?"

sell sb/sth short
to not give someone or something the praise, attention, or reward that they deserve
　Don't sell yourself short - tell them about all your qualifications.
au naturel--not wearing any clothes, or not wearing make-up, hair products etc that change the way you would naturally look

go for broke informal
to take big risks when you try to achieve something

Okay. I'm game if you are.
willing to try something dangerous, new, or difficult