__return_false() is one of a group of utility functions in WordPress that is helpful when you need an automatic result. In this case, calling the __return_false() function will result in a value of false.
This can be especially useful for filters that need a boolean, and you just need a false value.
// This will add a filter on `example_filter` that returns false
add_filter( 'example_filter', '__return_false' );
__return_false() is located in