I don't generally demand actual science from my movies. If spaceships screech as they go past the camera, well, perhaps that's what they sound like from the inside. And if Star Trek wants me to believe something called "red matter" can create black holes, I'm so there. The problem isn't with the red matter, whose science I don't understand. It's with the black holes. It's with ships escaping them, emerging from them. Huh?
In the woeful Generations, we had a guy make a star go nova in order to alter its gravitational effects. Except that gravity has to do with mass, and the star's mass would be unchanged. But at least we saw the star's explosion in real time when it should have taken light 20 minutes or so to reach the planet. So there's that.
Titanic's active fourth boiler notwithstanding, the one that bothers me most was in, of all things, Superman II: an astronaut on the moon tries to escape the bad guys by firing the lunar module's descent engine, not its ascent engine. Is this a nit? I say no. Anything that knocks me out of the reality of the movie into regular reality is a failure, no? You surely don't want my brain anywhere near reality when I'm listening to people talk on the surface of the moon.