I don't agree that Vizzini is trying to reason in logical absolutes. He talks like he is, but he doesn't necessarily believe the things he's saying.

Man in Black: You're trying to trick me into giving away something. It won't work.
Vizzini: It has worked! You've given everything away! I know where the poison is!

My interpretation is that he really is trying to trick the man.

Later he distracts the man and swaps the glasses around; then he pretends to choose his own glass. He makes sure the man drinks first. I think he's reasoning/hoping that the man would not deliberately drink from the poisoned cup. So when the man does drink he believes his chosen cup is safe. If the man had been unwilling to drink, Vizzini would have assumed that he now held the poisoned glass, and perhaps resorted to treachery.

He's overconfident, but he's not a complete fool.

(I don't have strong confidence in this analysis, because he's a minor character in a movie.)