Most of the times I see people trying to use "truth darts," they use them in RESPONSE to something that their wayward spouse has done or said (usually said).
And that's fine.
But even more powerful is when you deliver them out of the blue, proactively. At some point, Karen, I'd love to see you summon up the nerve to just walk up to your husband when he's sitting there alone, with no kids in earshot, and calmly say the above to him.