It's not gaslighting as it is not manipulation. The dad doesn't believe the son and there are accusations that the son is mentally ill, but this is perfectly reasonable in this situation, and this isn't done in a manipulative way.
Teenage boy is accused of being on drugs when he tried to tell people what is going on. It also part of his background to have an addiction. No drugs are actually taken during the film.
Flashing police lights in two back-to-back scenes. Starts in the next scene after one character cuts another character with a knife. No actual strobe effects used.
A teen takes off another teen's shorts underwater. Sex scene with two adults through a window and later closer up on a character's back. Two characters are shown naked from behind only.