Being Nice to a Point?

So, we all know it's good to be nice. Parents always tell children to be nice and kind to other people. However what if being nice to some one else takes away from your own happiness. For example someone asks you for a ride to a place that you're already going, the way you were raised might make you feel obligated to be nice and give them a ride. What if you don't really care for that person (you don't hate them but they're not your favorite person) and riding with them would make that trip rather unhappy, now lets say it's sort of a big event, for example prom and someone asks to ride with you and your date. It's kind of a long drive, you don't really care to have that person there, but you all are going to the same place. Should you still "be nice" and give that person a ride even though it might make you unhappy at kind of an important event at the time? I used to think, yeah you definitely should give that person a ride because how unhappy is it honestly going to make you, and part of being a good person is making a little self-sacrifice for others. Isn't that what many of us strive to be, Good people?However, someone told me a while ago, why should you do something for someone else if it takes away from your own happiness? I honestly don't know, while it is always good to help people, you don't want to make yourself unhappy. We can apply this to almost any situation when we are asked to do something or feel obligated to do something for someone else. For many situations it really may not be a big deal or bother you to do something nice for someone else. And who knows they may really have needed that extra act of kindness. I guess you have to look at the pros and cons of each situation and determine for yourself, how the level of unhappiness of an action affects the amount of kindness that would come from that action and how it affects yourself. Then again maybe you should just be kind for the sake of being a good person? Think about it.