i) Lie down and start humping the floor, as a joke.
ii) Explain to the dude that he had used too many exclamation marks in his order.
iii) Use the card I would have in my hand if I was about to pay for something as a shuriken to throw at the dude, which would give me enough time to acquire a keyboard to beat him with.
I got robbed at gunpoint in the street about a year ago, and I'm ashamed to say I just did exactly what they asked and handed over my cash and phone. You may think you would have tried to disarm them, but when the gun is pressing into your neck and they have motorcycle helmets on... well, it's not that straight forward.
Anyway, if people were getting shot it might be a different story, but really it's not worth getting involved over a few material things.