I remember in Revenge of the Sith, when the actor playing Vader yells "nooooooooo", at what is supposed to be the emotional climax of the trilogy, the theater roared in laughter.
The Titantic. In the scene when the dude falls off the back of the ship and hits the propeller on the way down. He hits it with a solid clang and someone in the theater loudly goes “oooooohh that’ll leave a mark…”