I must point out that “whenever they want to be nice to someone” entails a desire to be nice to someone. Your very phrase defines it as being in their interests to be nice to someone. Rationalization isn’t even necessary here. You wanted to do something—you did it. Selfishness isn’t that complicated.
My guess would be that this individual had read Atlas Shrugged and hadn’t fully understood what selfish meant in the context. Ayn Rand was setting out to redefine the word, not to glorify the “old” meaning.
Jacob—going into detail about why atheists are evil, violent, pornography-loving, science-worshiping people doesn’t disprove their worldview. (And I find it interesting that you claim that atheists go into science, rather than scientists choosing atheism—but then, you don’t seem to know what science is, so this shouldn’t surprise me.)
Incidentally, out of eight models for quantum mechanics, at least two continue to permit determinism, which, notably, is another thing you erroneously attribute to atheism. One, neo-realism, of which Einstein was a follower. The other, multiverse theory. One of many matters on which you get your facts entirely wrong.