Watch horror movie "The Final" from 2010. It's about a group of bullied kids (many of them obviously incel) who invite their bullies to a secret house party, drug them and then torture them, while taping the whole session. It's a great movie, showing all the desperation and misery following someone who is an outcast.
"Rampage" (mentioned above) is also a good movie, personally I like first and second part more than last one. It's not exactly about incel and it's more politically-motivated type of movie, but it's great because there are many scenes of rampage and massacres on normies and stuck up sluts.
"We need to talk about Kevin". Great film and great piece of art, showing misanthropic and psychopathic kid going on rampage in his school, and aftermath of his mother's life after the massacre.
Really any movie that is about school violence and school massacres/shootings. There are many of this, just search on google and you'll see. There was also movie "Del Playa" loosely based on Elliot Rodger and his Isla Vista massacre, altough I'm not sure whether it was released or not.