As a general rule, not just for taking safety cards:
if you are nice towards the cabin crew they´ll be nice to you.
- speak to them by their name
- say "please" and "thank you Mr./Ms. XYZ"
- move yourself to the galley to get your extra drink in the middle of a red eye, and chat a little when you´re there
- treat them as a human being rather than like a lower form of life which are just there to serve drinks
they can give you some treats, like
- responding faster when you ring the bell
- giving you an extra meal
- giving you a package of 10 mint safety cards rather than the one torn one from your seat pocket
- negotiate a cockpit visit, even on a US airline.
And yes, all these reactions posted actually happened to me.