...
It is axiomatically the case that all action is self interested. The idea of a non self interested action is a paradox. the fact that you have taken an action is its self proof that you believed the action was in your interest.
Consider the following (Let's call "good stuff" hedons, even though it's imprecise):
1. Perceived self-interest --
An act which the actor believes will maximise hedonic value, but in reality does not. (investing in a stock that tanks)
2. Short-term self-interest --
An act which offers immediate gratification, but is known by the actor to reduce overall hedonic value. (shooting dope, smoking crack, being lazy etc., etc.)
3. Irrationality --
"My liver is bad, but i won't see a doctor. Because fuq, that's why!" (Dostoevsky posts on 4chan)
And, of course, there's your definition of self-interest. If self-interest is axiomatic, then it's axiomatic. When you start with a given that all actions are motivated by self-interest, there's nothing left to prove.