Well it isn't so much bad, as impossible.  The compiler won't let you do it
and it doesn't make any sense.

eg

class MyClass {

   public void methA() {}

   public static void main(String[] args) {

       methA(); // illegal, you need an instance
                // of MyClass to call an instance method

       new MyClass().methA(); // legal, we have an instance.
   }
}

on the other side of the coin it is legal to call a static method from an
instance, but it is bad practice, since it is misleading.

class MyClass {

   public static void methB() {}

   public static void main(String[] args) {

       methB();         // legal, MyClass is implicit
       MyClass.methB(); // explict version

       MyClass inst = new MyClass();
       inst.methB();    // legal, but bad. [1]
   }
}

[1] This is legal because the compiler says, I know that 'inst' is an
instance of MyClass so I know how to call the static method.  But it is
*bad* because it looks like you are calling an instance method, so is
misleading to the maintainer.  Obviously it is also a waste of resources
instantiating the object, but the usual times people do this is when they
have the instance anyway.

--
Mike W