if you are doing something for the sole reason to get something back, then you are doing it for the wrong reason. you are an asshole. whatever happened to chivalry? why can't we do something for someone for the simple reason of making someone's day a little easier?
Stefan Lundqvist i agree, but to cause harm to someone who doesn't is just stupid. you never know what is going on with that person. the world is full of rude people, it is also full of people who are having a bad day, or have their minds on other things, or don't speak your language. just hold the door open for people to be nice, if you get a thank you, great, but to dwell on the non thank yous is just ridiculous.