I wouldn't say I've made up an entire movie because of it, but I have very widely missed what a movie was from its trailer.
Kung Pow! Enter the Fist had such a shit trailer, I had no interest at all in seeing it. The only reason I did, was because my siblings wanted to go and my mom didn't wanna drive so she paid me to take them. Had I known it was a comedy and how they made it, I would have actually been hyped. That shit was the funniest movie I ever saw up to that point.
From the trailers I remember seeing at the time, I just thought they had simply brought an old kung fu movie that was only in Chinese or something to the US for the first time with English dubbing. And it didn't look like a particularly good kung fu movie. They did absolutely nothing to make it look like a comedy, with the gag being that they were just riffing on an old kung fu movie.