Satan's two oldest sons are angry that he has decided to stay in power for another ten thousand years denying them ruling hell, so they choose to make Earth their kingdom. The two sons are played by Tiny Lister and Rhys Ifans, dad Satan is played by Harvey Keitel. To turn Earth into their personal hell they cause problems in New York City by lowering the drinking age to ten and inciting a general state of mayhem. All this will lead to Satan's death unless the renegade sons are stopped. Then we are treated to scenes of ten year old boys throwing up, a demon with breasts on his head and an hour and a half of Adam Sandler's fake speech impediment.
Potty humor is fine when it's funny.
Little Nicky is a group of unfunny R-rated gags strung together to make a long movie. Most likely because it's a big studio picture. Several parents at the screening I sat through did.