If, while I'm on your website, I click a script-controlled object pretending to be a menu, and it pops up another element pretending to be an open menu, it should go away again on another click. That's called "toggling" a state. It should NOT cover the entire page, obstructing other content forever until I finally reload the whole damned web page just to get rid of it. This is especially important when your elements pretending to be menus are opened by a mere mouse_over event, rather than a mouse_down event on a trigger object.
As a related point: your so-called "responsive design" might want to be responsive to the fact that I might be using a touch interface, rather than a mouse, and STOP with the useless rollover effects and, more importantly, dispense with the requirement of a rollover event as a trigger for functionality!
Please insert $50.