I don't know about the rest of y'all, but for me it's spare the ROCK (as in rock-n-roll), spoil the child.

But seriously, I think it means if you don't discipline your children when they misbehave, you end up with entitlement brats who won't listen when they're older.
I agree! I read this at a juvenile court clerk's office the other day (I was working):
How to raise a criminal:
1. Begin in infancy to give the child everything he wants. In this way he will grow up to believe the world owes him a living.
2. When he picks up bad words, laugh at him. This will make him think he's cute. It will also encourage him to pick up cuter phrases that will blow off the top of your head later.
3. Never give him any spiritual training. Wait until he is 21, and then let him decide for himself.
4. Avoid the use of the word "wrong." It may develop a guilt complex. This will condition him to believe later, when he is arrested for stealing a car, that society is against him and that he is being persecuted.
5. Pick up everything he leaves lying around - books, shoes, and clothing. Do everything for him so he will be experienced in throwing all responsibility onto others.
6. Let him read any printed matter he can get his hands on. Be careful that the silverware and drinking glasses are sterilized, but let his mind feast on garbage.
7. Quarrel with your spouse frequently in the presence of your children. In this way they will not be too shocked when the home breaks up later.
8. Give the child all the spending money he wants. Never let him earn his own. Why should he have things as tough as you had them?
9. Satisfy his every craving for food, drink and comfort. See that every sensual desire is gratified. Denial may lead to harmful frustration.
10. Take his part against neighbors, teachers, and policemen. They are all prejudiced against your child.
11. When he gets into real trouble, apologize for yourself by saying, "I never could do anything with him."