Happiness pump
The happiness pump is a way of showing problems in utilitarianism.  Utilitarianism is a moral philosophy.  It is a way of deciding which actions are good and which are bad.  In utilitarianism, actions that make more happiness or stop pain are good.  Actions that stop happiness or make pain are bad.  In utilitarianism, it does not matter who is becoming happier or feeling less pain.  That means that, in utilitarianism, helping strangers is good.  The happiness pump is a person who has taken utilitarianism too far and will give themselves lots of pain so long as they believe it makes other people somewhere in the world much happier.