Used in the early days of American Idol when the world was new to the competition and Simon Cowell was the biggest douche bag on the planet. This phrase can be used the same way as Don't be a dick!
Dad: Thanks for making this wonderful breakfast kiddo.

Son: You're welcome dad.

Mom: ...I don't know..the pancakes were a little dry and the eggs were undercooked..and don't get me started about the-

Dad: Dammit babe, Don't be a Simon.
Get the Don't be a Simon mug.