Q: What did the mommy rope say to the baby rope? 
A:  “Don’t be knotty!”

Explanation: When you tie a rope you make a knot.  To behave badly is to be naughty (naw- tee); it is a word that is used with small children.  “Knotty” sounds like “naughty” and “naughty” is a word that a mommy might use with her child, like in the joke!  Be good; don’t be naughty!