If someone is sick, bring some soup. Don't ask if they want soup so that the sick person has to say, "Yes, bring me soup." Just do it.
If it's someone's birthday, just buy a gift or birthday cake if you're willing to do it. Don't ask if they want a gift or a birthday cake, so that the person has to say, "Yes, buy me a cake."
Don't make people ASK YOU FOR A FAVOR. If you were already inclined to help someone out, just do it, without putting the burden on the recipient.
If you really didn't want to help out that person, and you just asked them to show how nice you are, knowing full well they would say no, don't be a jerk.