I couldn't disagree more. "Self interested" absolutely does not have a well understood meaning in casual, every-day conversations. It's one of the most ambiguous terms out there.

Try this out: at a dinner party (one that you don't care if you're invited back), declare that "all people act out of self-interest, ultimately."

Odds are good that two people will disagree quite vehemently about this, and at the core will be a fundamental disagreement about what it means to be "self-interested".