Some people are so grateful to me and they say thank you all the time?

If you are not willing to accept sincere thanks from grateful people, then you appear to feel superior to them. If whatever you do is nothing in your view, you are basically insulting them. It would be better not to do anything at all than to feel as though you are in some way better than the people you help. They are not thanking you to entertain you, so if it bores you, that's just too bad. You are on some kind of ego trip.