What Does "Plastic Banana" Mean?

CALLER: Twenty-eight-year dittos.  I've been listening to you since the beginning, August '88. You've got a phrase... This is a perfect Open Line Friday call, by the way, 'cause I'm not gonna talk politics. You got a phrase you've been using for those years: "phony baloney, plastic banana, good-time rock 'n' roller." ... Where on earth does the term "plastic banana" come from?