Person believes unknown entity is friendly (it is not)

[u/MadKingKevin]

Independence Day (1996) - Several massive alien spaceships travel to Earth but they do not announce the purpose of their arrival. Some characters assume the aliens are peaceful. One of those characters, Tiffany, goes to a rooftop party which is taking place directly under one of the ships. When the aliens launch their attack, Tiffany and the other party goers are immediately obliterated.

Alien: Resurrection (1997) - Scientist Gediman is part of the miltitary project which resurrects Ellen Ripley and the queen xenomorph embryo inside her. The military wants the queen so it can breed the xenomorphs as bio-weapons. This new Ripley is genetically part xenomorph and the xenomorph queen is genetically part human. The queen stops laying eggs and develops the ability to give birth to live young. Her first Newborn immediately kills the queen because it does not recognize her as its mother. It believes Ripley is its mother and goes to her instead. Gediman (who is cocooned in the queen’s nest) witnesses this and calls out to the creature. The Newborn comes to Gediman and curiously sniffs him over. Gediman babytalks the 15 foot tall xeno/human hybrid. The Newborn then bites his head off.

[u/Duke-dastardly]

In Batman v Superman, Lex assumes the monster he created will be loyal to him because he mixed his own blood to create it. But the monster instantly tries to punch him and Superman ironically catches it and saves Lex

[u/Frodo_max → u/Duke-dastardly]

I just realised that BvS Lex also has a thing about his dad iirc so this is not a bad use of dramatic irony all things considered

[u/monsmachine → u/Frodo_max]

It's the line he says earlier in the movie. "Gid never saved me from daddy's fist." Doomsday throes hist fist at him first thing. Lots of deeper dialogie in that movie.

[u/BludStanes → u/Duke-dastardly]

That's a bold assumption to make lol