Film: Star Wars Episode V: The Empire Strikes Back
The Empire Strikes Back is easily one of cinema's most beloved blockbusters and with good reason. Both a relentlessly thrilling spectacle and a surprisingly emotional story of good vs. evil, Empire is a masterpiece of commercial cinema and every sequel out there still tries to copy it to this day. For the most part, that is a good idea but there's one scene which absolutely mustn't be mimicked: the infamous brother-sister kiss between Luke and Leia.
Leia kissing Luke to make Han jealous wasn't a necessary moment to begin with, but when it's revealed in Return of the Jedi that they're brother and sister it becomes incredibly uncomfortable to watch. It's not precisely clear when George Lucas decided on the plot twist about the Skywalker twins, but if he'd decided on it before writing this scene, then it's a real mystery as to why it was left in.
This is one of the most notable bad scenes in great movies ever and an unbearably cringe-worthy moment which really drags down an otherwise great sequel.