Wow. Just watched this for the first time and I can't remember a more cold-blooded, vicious death for a monster!

The whole family poisons him with some ammonia-based chemical and then circle him in a helicopter laughing hysterically as he slowly collapses, twitching and gasping. Then the camera lingers on his dying body as his muscles twitch randomly and his rectum bleeds. Only the little boy has misgivings about this, and the adults have to choke back their laughter while condescendingly patting him on the head.

And I know the above is all spoilers, but hey, come on.