The silver spray paint in universe is basically preparing yourself to enter heaven (Valhalla) "all shiny and chrome", implying that being shiny and chrome is a higher state of being than being rusty and covered in dirt, which makes a hell of a lot of sense in universe. This particularly shows up in the difference between the leaders' cars (e.g. Immortan Joe) and the War Boys' cars. The War Boys are essentially on a death clock due to illness, so they act as suicide fighters. The Psychotic flash bang was really effective in communicating the cult of personality that Immortan Joe has cultivated. I really liked it because the world building was incredible IMO.