Psychological egoism claims that whatever we do, we do out of self-interest. Give an example of an act that does not seem to be done out of self-interest and explain how the psychological egoist might try to interpret that act as selfish.
As an example of an action that does not seem selfish, let us imagine that I go to pick up my kids from school every day. We play on the playground for a while after school and I swing one of my daughters in a certain way that she enjoys. Other kids (who are not even friends with my daughter) ask me to swing them in the same way and I do so. This seems to be something that I am doing that is not in my self interest.
But a person who believes in egoism could easily claim that I am acting in my own self interest. For example, they could say I am doing this because I want the kids to think that I am a nice person. They could say that I am doing it because I want to teach my kids to be generous, thus making my kids more likable. They could say that I am doing it because I believe God wants me to and that I hope to gain a place in Heaven by acting well here on Earth. Any of these would be selfish motives that I might have for doing this seemingly selfless act.