From Songfacts:
Shouting out “Free Bird!” as a request at concerts became a rock and roll joke, and every now and then a musician will actually play it. The 2007 Mitch Myers book The Boy Who Cried Freebird: Rock & Roll Fables and Sonic Storytelling explores this subject in a work of fiction about the first person ever to shout “Free Bird” at a concert.
Here are two cartoons on it.