What's the best way to introduce programming to a friend?
Someone who doesn't know what the calculator can do.

Show them a game or two, basically. If you get some BASIC games, you can show them some source and that will tell them they could make things like that too, if they are interested in such things. Show them some ASM games, and that might produce even more interest. And of course, tell them that programming concepts they learn on a calculator can be applied to other languages for computers and mobile devices as well.

What if you find out they know more programming than you do?

Well then you learn from them and you both experiment with programming the calculator. Just have fun!

And if they don't care about programming or you, then what do you do
?

Then you have them show you stuff. Or you talk about your shared knowledge. It's really not a big deal when someone knows more about something than you.

Stop being friends with them seems the obvious answer. If someone doesn't care about you, don't waste your time caring about them.