Altruism

Altruism is tricky. In order for an act to be truly altruistic, you can't talk about it. As soon as you do, someone can argue that you only did it so you could brag about it.

Richard Alexander, an evolutionary biologist known for his work on the origins of morality, describes an argument he had with his mentor. Alexander was trying to make a case for pure moral motivations, and he described how he went out of his way to avoid stepping on a line of ants. Isn't that truly altruistic? And his mentor responded: "It might have been until you bragged about it."

Paul Bloom, Psych, 251

I guess the solution here is to always talk about these things in a hypothetical sense. But if you do that, you can't actually prove that anybody ever does this.