Now you have to post the full convo because right now I'm imagining an awkward silence and she backing away slowly.
I've known the girl for years, we used to work together until I left that place about 3 years ago. I taught her accounting and she worked under me (

), she's about 25 or so, I'm 30. We catch up for social drinks or lunch about every month or so. So I know her reasonably well.
I rang her with an incredibly lame line, something like: "would you like to go out for dinner, but only if you bring your awesome calculator". She had been telling me all about it the day before at drinks. Accounting joke.

We laughed a bit, she said "what did you have in mind?" I felt relief and my heart pounding reduced from jackhammer-level to mild earthquake-level.
I said "I didn't think that far ahead, but I'll email you with some ideas next week and then you can suggest somewhere else and we'll go there". Another lame joke based on our history.
Laughed a little more, said goodbye. Emailed her this morning and she's still interested. Score.