Comic Sans font. You do not want this font anywhere near your menu. It’s reserved specifically for elementary school teacher newsletters. And there’s a documentary against it.
Paryrus font. This font is the stereotype of stereotypes for Greek restaurants. (There’s even a blog about the overuse of this font.) If you’re truly Greek and serve a mean gyro, you deserve something more creative and easier to read.
Dollar signs. Want to scare off your customers from the higher-profit items? Just attach a dollar sign to the price. There’s even a study to back this up. Read it right here.
Clipart. If you’re using the Microsoft Windows clipart collection to illustrate your menu, stop right now.
Too many pictures. When you have too many pictures on a menu, the customer doesn't know where to look or what to eat. Your menu and your servers should guide the customer on what to eat, not leave them hanging.
Did I miss anything you would never want to see in restaurant menu design?