FRANK COSTELLO IN THE DEPARTED (2006)
Boston gangsterdom. For years Frank Costello (Jack Nicholson) stays one step ahead of the Boston police. How is this possible? Dude is an informant for the FBI, throwing other gangsters under the bus to save his own ass. Cold, man. Just cold.
Punishment for snitching:
He gets gunned down by his pupil and staff sergeant, Colin Sullivan (Matt Damon), after he thinks Costello might have mentioned him to the Feds.