This.

It borders on arguing about the meaning of words, so I find it useful to describe what I mean by "lying", i.e. "conveying information that adjusts someone else's worldview away from reality". Funnily enough, that excludes most lies-to-children..

At that point whoever I'm talking to will either point out that his definition differs, or even decide to go with mine henceforth, and either way we can start getting some real work done.