There are big holes in your implementation. Sure, $selfmirage->{'washhands'} contains a closure, but all the closure does is call a global subroutine with the private data as argument.

All $dirtyeater needs to do is to replace Dinnerclosure::washhands with a sub of his own, and $dirtyeater can modify handsclean all he wants. See the following test code:

#!/usr/bin/perl
use strict;
use warnings;
use Dinnerclosure;

my $dirtyeater = Dinnerclosure->new();
{
    no strict 'refs';
    no warnings 'redefine';
    local *{"Dinnerclosure::washhands"} = sub {
        my $obj = shift;
        $obj->{'handsclean'} = 1;
        print "I didn't really wash my hands\n";
        return 1;
    };
    $dirtyeater->{'washhands'}->();
    $dirtyeater->{'eatfood'}->();
}

__END__
I didn't really wash my hands

You washed your hands -eat all you want
[download]

$dirtyeater didn't wash his hands - he just pretended to. But he still was allowed to eat.