Neil was a terrible person
I had no sympathy for Neil after what he did to the mentally handicap child. While the film "brushes off" the nature of what he did, in reality the result of setting off bottle rockets in someone's mouth would result in severe burns that would hospitalize and permanently disfigure the child. And this is Neil's idea of "having some fun". I found this to be the most disturbing scene in the film.
Neil is no different than other notorious psychopaths that were abused as children. Look up the definition of psychopath, Neil fits it rather well. Wendy said he doesn't have a heart and the film shows he has no empathy.