Please Caramelize The Onions - Sticker

Is this a joke or a literal command?!?!?! Why is it so funny?!?!?! Did I miss a culturally significant movie where the "onions" were not "caramelized"? Please send help.

* Durable & weatherproof * Made of thick vinyl which protects from scratching, rain & sunlight * Size: 2.8" x 2.8" inches