When you ask somebody to try their own hand at something before criticizing your efforts, you have violated Ebert's Law and lost the argument. Roger Ebert is not a filmmaker, but he knows what he likes and doesn't, and has every right to say so. Similarly, people don't need to be chefs to recognize a good restaurant, or musicians to appreciate a symphony.
Person 1: Your story is rubbish!
Person 2: I bet you couldn't do better!
Related to Lloyd Webber's Law Of Temporal Positioning. The law states taht people who arrive at a theatre after their performance has started will always have seats in the middle of a row, causing as much annoyance for the other theatregoers as possible.
The Lyttleton Theatre at the NT (London) seems to know which theatregoers will be late, and invoke Mackintosh's Corollary on purpose.