I grab the popcorn box, put it on my lap and spend the next few minutes casually sharing it with her. I would have been 16 or I am 25 and I just got a boner from reading all this talk about getting boners. All the while I'm poking a hole in the bottom. She reaches in and squeezes, looks up at me and says " My dick wasn't in those salty, buttery kernals for more than 30 seconds before he came and sat down to say a quick hello. If he had just asked me to touch his penis I probably would have.
I suppose ideally she goes to the restroom just before the previews so you have time to get things ready.
It took a while for her to actually realize it. She reaches in and squeezes, looks up at me and says " Ever think that, had you just put your damned dick in the box, you mighta gotten yourself a handy. Stop asking where my penis went! Since this has come up a lot, this was a decade ago, I'm 30 now, and I'm married.