Where did s/he get that???
That's a common question and most likely they learned it from somewhere and even though teens may not want to admit it, lots of times they got it from their parents.
Even as children/teens learn things from peers, television, or other sources, there is an aspect of the behavior they learned from their parents.
You can learn a great deal about yourself from watching and listening to your children.
"Do as I say, not as I do," just doesn't cut it. Well children may/will learn a great deal from other sources, much (but not all) of their foundation comes from their parents and/or those who raised them.
You can learn a great deal more on this subject by typing: "children as reflection" in the Google Parenting Search Engine below.