What is the origin of the expression "This is not my first rodeo ?"

"This ain't my first rodeo" is how it's usually styled. According to Forbes' "SAPVoice" contributor Jonathan Becher, the earliest use of the phrase (or its variant) seems to be the 1981 movie "Mommie Dearest," when Joan Crawford (portraying Faye Dunaway) says, "This ain't my first time at the rodeo!"

http://www.forbes.com/sites/sap/2015/04/22/this-aint-my-first-rodeo
https://www.youtube.com/watch?v=xmczkkw6OZI

Becher notes, "The phrase isn't in the book that the movie was based on and I couldn't find any evidence this scene happened in real life. As such, the quote should probably be attributed to Frank Yablans, who wrote the screenplay."